In 2019, Leoncio Alonso González de Gregorio y Álvarez de Toledo, the 22nd Duke of Medina Sidonia, stormed into his late mother's palace on the Andalusian coast of Spain.

In a video he posted on YouTube marking the occasion, the Duke, tall and silver-haired, strides triumphantly through the Ambassador Room — a grand hall nearly 33 yards long, lined with oil paintings by the likes of Velázquez's master, Francisco Pacheco. In happier times, the room had been used for receiving dignitaries who visited the Duke's mother, Luisa Isabel Álvarez de Toledo. Celebrated as the "Red Duchess," Luisa Isabel was a socialist-minded, fascism-battling aristocrat beloved by ordinary Spaniards. But now, 11 years after she had cut Leonicio and his siblings out of their inheritance, the Duke had arrived at the palace to lay claim to a national treasure he considered his by birthright.

"At last, I'm at home after many decades away," Leoncio proclaims in the video.

The treasure, known as the Archive of Medina-Sidonia, was housed in the palace's attic. A collection of 6 million documents, it spans nearly a millennium of Spanish imperial history. Within its pages lie the secrets of the kings, dukes, and explorers of medieval Spain. Luisa Isabel, who had spent the last two decades of her life cataloging the archive, believed it proved that Arab Andalusians, not Christopher Columbus, had discovered America. Perhaps the most important privately held archive in Europe, it is valued at over $60 million, though historians who have studied it consider it priceless.

Luisa Isabel, who'd been imprisoned under the regime of dictator Francisco Franco, believed the archive should pass to the people. "I have inherited this legacy, which is legally mine," she once declared. "But morally, it belongs to everyone." In her will, Luisa Isabel left only 743,000 euros to Leoncio and his siblings, Pilar and Gabriel. The bulk of the estate — including the archives — would be controlled by Liliane Dahlmann, Luisa Isabel's lover and longtime secretary, whom the Duchess had married on her deathbed.

What ensued was a bitter legal battle that would shatter the family, captivate Spanish society, and throw the fate of the archive into doubt. Leoncio's homecoming video was a declaration of war. Flouting a court ruling that barred him and his siblings from living in the palace, he had decided to move back into his ancestral home — even though it was legally occupied by Liliane, his mother's widow. "There's a lot of tension," says Gabriel, the black sheep of the family. "They barely talk to one another, enter and leave through separate doors, and rarely bump into one another." To drive home his disputed claim, Leoncio made a point of interrupting weekly palace tours. "Welcome to my house!" he would greet groups of startled tourists. "Here, they only manipulate the truth."

Liliane, ensconced upstairs with the archive she had been charged with safeguarding, kept her silence. At times it must have seemed that the family's inheritance, passed down through the generations and now entrusted to her care, was cursed. "Sometimes you don't choose your destiny, it chooses you," she once said. "Personally, these past few years have been exceedingly difficult — the stuff of nightmares."

The family appeared to start off happily enough. In 1955, only 18 years old and already pregnant with Leoncio, Luisa Isabel married José Leoncio González de Gregorio, a nobleman from Soria. Photographs from the time show the new Duchess smiling in a black ankle-length dress, her long hair framing her tiny face and her lips brightened with lipstick. Standing beside her, José Leoncio appears tall, athletic, and handsome.

In reality, Luisa Isabel and José Leoncio couldn't have made a more ill-suited couple. Her ancestors had commanded Spanish armadas, served as prime minister, and owned vast swathes of southern Spain. Her parents had fled the country during the Spanish Civil War. Her new husband, by contrast, was a die-hard conservative who supported Franco's dictatorship. Luisa Isabel loved the night life. José Leoncio, a man of the countryside, disliked high society nearly as much as the radical ideals that would soon claim his wife.

During their brief union, the couple had three children in quick succession: Leoncio in 1956, Pilar in 1957, and Gabriel in 1958. But the Duchess never seemed to take to the role of mother. After giving birth to Gabriel, family lore has it that she handed him to the nurses and declared she had fulfilled her role as a woman. The moment also marked the end of her marriage. Within the year, she had separated from José Leoncio and began to spend long stretches in Paris, where she mingled with Simone de Beauvoir and other leading intellectuals. Her children remained behind in Madrid, where they were left in the care of Luisa Isabel's grandmother. "She rarely came to visit," Gabriel recalls.

One day, when Gabriel was 6 or 7, his mother appeared at the door. Gone were her elegant dresses and long hair. Wafer thin, Luisa Isabel now sported men's trousers and short-cropped hair. There were rumors she was sleeping with women. "Someone in the household said she was our mother," Gabriel recalls. "But for us, she looked like the boy who worked at the local grocery." Leoncio was distraught. "You're not my mother!" he cried.

The change in Luisa Isabel ran deeper than fashion. In 1964, the Duchess led a protest march of fishermen in Sanlúcar. Her noble pedigree gave her a measure of protection to speak out against Franco. "This privileged aristocrat had a rebellious spirit," as one newspaper put it. Her reputation was further cemented in 1967, when she stood up for a group of protesters whose homes had been rendered radioactive after an American nuclear bomber crashed over the small fishing village of Palomares. The protesters, she told soldiers dispatched by the regime, "are here only for justice, and they are here with me." She then led the group to a bar at the village's main square for a round of cold beers.

Arrested and thrown in prison for a year, the Duchess kept up the fight from her miserable, rat-infested cell. She wrote letters and articles denouncing the conditions in Spanish prisons. A novel she authored about suffering farm workers called "The Strike," which she had managed to smuggle into France, prompted the government to threaten her with a 10-year sentence for slander. In April 1970, a few months after her release, the Duchess escaped to France disguised as a man. "I remember putting the hat and the mustache on her," recalls Julia Franco, a longtime family employee.

During her exile, José Leoncio seized on her political dissidence to secure custody of the children. "The role of being a mother slipped away from her," Pilar recalls. According to Gabriel, he and his siblings were at their father's mercy. "He was determined to redirect our lives, banning the staff from passing her calls or letters on to us," he says. The children, by birth, were nobility. But their lives felt anything but noble.

"The Red Duchess Returns" blared a headline in El Pais, a national newspaper, in 1976. Franco had died, paving the way for Spain's first open elections in four decades and the safe return of Spanish dissidents. Luisa Isabel moved into the palace at Sanlúcar, where she held court each evening surrounded by famous actors, foreign journalists, and celebrated academics. No longer closeted about her sexuality, she came across like a Spanish version of Sid Vicious. "She was punky, with short, spiky hair and worn-out clothing," recalls Miguel "El Capi" Arenas, who lived with the Duchess in the early 1980s.

By day, Luisa Isabel devoted herself to organizing the archives. Often rising at 6 in the morning, she would sequester herself in the attic among stacks of dusty documents, chain-smoking cigarettes — two packs a day — and barely eating. She spent years cataloging the papers in jaundiced folders, tying them up with string and developing a knack for deciphering their Gothic cursive handwriting, with all its loops and ligatures. Establishing herself as an amateur historian, she published a dozen books, including "It Wasn't Us," her reappraisal of Columbus published on the 500th anniversary of his arrival in America. Historians came to admire her patience and diligence. "She did a magnificent job with very few resources," says Juan Luis Albentosa, chief archivist of the Franciscan Library in Murcia. "She had no state support back then, nor any formal training."

The Duchess had first encountered the papers in the late 1950s in a storage tunnel at her family home in Madrid and transported them to the palace in Sanlúcar in the back of a lorry. While it wasn't unusual for noble families to maintain private archives, this one encompassed the unwritten history of Spain itself. The archive contained not only the records of various aristocratic families, but also receipts signed by the painter Diego Velázquez, primary sources about the Spanish Armada, and municipal records from Palos de la Frontera, the village from which Columbus set sail in 1492.

The Duchess both embraced and defied her status as an aristocrat. She believed the Archive of Medina-Sidonia belonged to the public — but only after she was no longer alive to claim it. "She was a traditionalist," her nephew, Alfonso Maura, tells me. "How could she spend all those years working on the family archives and not be?" Andres Martinez, a historian and friend of the Duchess, casts her contradictory nature in more poetic terms. "You can't jump out of your own shadow," he says.

As Luisa Isabel devoted her days to the archive and her nights to her soirees, her children saw her only occasionally. To the Duchess, they were reminders of their father — and of the world of entitlement she had devoted her life to rejecting. In 1977, a year after her return to Spain, she wrote to the director general of the Spanish National Heritage Board to request that the palace and its contents, including the archives, be registered as protected public goods, to "prevent losing what belongs to everyone."

"My family's wealth isn't important, and my children don't seem interested in preserving our artistic heritage, although they enjoy it," she wrote. By the following year, the request had been granted. The most important and valuable asset of Medina-Sidonia's ancestral heritage was now under the protection of the state.

In Gabriel's view, "the moment that marked our disunion" occurred in 1982 — the day Leoncio married his first wife, a Catalonian aristocrat named María Montserrat Viñamata y Martorell. It was at the wedding that Liliane Dahlmann, one of the bridesmaids, entered Luisa Isabel's life.

The Duchess noticed Liliane immediately. Tall and blonde and 20 years Luisa Isabel's junior, Liliane had moved from Germany to Barcelona as a girl. "I'll make her mine," the Duchess told her friend Capi Arenas during the reception. Julia Franco, who was also in attendance, recalls that the Duchess and Liliane "couldn't take their eyes off each other."

Before long, Liliane had moved into the palace, where she served as Luisa Isabel's secretary. The relationship mellowed the Duchess. Gone were the wild parties and the bohemian friends crashing at the palace for months on end; Luisa Isabel became quieter and more dedicated to the archives. "They were always together," her friend Andres Martinez recalls. "I couldn't get the Duchess alone, ever." Luisa Isabel's children were also suspicious. "Liliane was always in my mother's ear, trying to make us look bad," Pillar says.

The children also began to fight among themselves. As the eldest, Leoncio had a role in deciding which family titles went to whom. Gabriel claims they had an understanding that he would be named Duke of Montalto and Aragon, and that Leoncio had changed his mind.

"I'm inclined to stop the progressive scattering of our family titles," Leoncio wrote in a letter to his brother, rationalizing the decision. Since the family could no longer claim economic or political power, he said, "moral and historical integrity is all we have left."

Pilar was next. In 1993, King Juan Carlos I had named her Duchess of Fernandina. Now, Leoncio maintained that the title should have gone to his son. He launched a battle in the Spanish courts, stripping his sister of her noble name and privileges.

Leoncio also squabbled with his mother over the estate of her grandmother, who had left the children an inheritance "worth millions of euros," according to Gabriel. But as the estate's administrator, the Duchess had spent much of the money. In a letter to his mother, Leoncio protested this "robbery," complaining that he had received no financial help after his marriage and the birth of his son. He barely mentioned Pilar and Gabriel. The Duchess, in a scathing reply, denounced Leoncio as "weaker" than she had "ever imagined."

Gabriel had considered himself and Leoncio thick as thieves; they had lived together during their university days in Madrid and always looked after each other. Now, he felt that Leoncio was only looking out for himself. Pilar agreed. "My older brother tried to keep everything for himself and push us out," she says.

Gabriel and Pilar took the nuclear option. In 1989, they successfully sued their mother over the misspent money. In retaliation, the Duchess banned them from the palace.

Over the ensuing years, the Duchess sold off various tracts of land and other assets, reinvesting the money in the palace, and took steps to ensure that none of the children would have any power over the archives. In 1990, she transferred ownership of the palace and the archives to a new organization she founded, the Casa Medina Sidonia Foundation. And in 2005, she amended the foundation's statutes to ensure that, upon her death, Liliane would take over as president.

Three years later, on the night the Duchess died — March 7, 2008 — mourners filled the Salon of Columns, a vast room in the palace crafted by American artisans provided to the family by the 16th-century conquistador Hernán Cortés. Gabriel arrived at around 10 o'clock at night. At age 50, he and his mother hadn't spoken in 20 years. Leoncio and Pilar were already there. The greetings between them were civil but not warm.

There were whispers about how the Duchess had carried out one final snub of her children. Just 11 hours before her death, she had married Liliane in a civil ceremony. Details of the wedding were hush-hush, but it granted Liliane legal control of the palace — and the archives.

Gabriel had arrived at the palace with a somewhat macabre mission in mind. He'd brought a camera with him, and he planned to capture an image of his mother's corpse, just as he'd done when his father had died a month earlier. He wasn't sure where this impulse came from. Perhaps, after years of animosity and neglect, he wanted proof his parents were really gone for good.

Stepping away from the mourners, Gabriel entered the room where the Duchess lay in a casket. She was "deteriorated, stiff," he recalls. He felt no despair, no sense of grief. He took the camera from his pocket and held it over her body. As he did, others in the room protested. Gabriel took the picture anyway. "He had the right to take a photo of her," says his friend Íñigo Ramírez de Haro, an author and playwright who accompanied Gabriel that night. "He was her son, after all."

Alerted to what was happening, Leoncio suddenly appeared and began chasing his brother around the room. "He asked me to delete the photo," Gabriel recalls. It was a regression to youth, two middle-aged men sparring like adolescents in their mother's grand house. It was also a sign of the quarrels to come.

At first, the siblings worked in concert to challenge their mother's will. In court, they cited a provision of Spanish law mandating that a person's descendants have a right to two-thirds of an estate, regardless of the deceased's wishes. "I'm not surprised by any of this," Gabriel told a reporter at the time. "My mother made it clear that she was going to fuck us."

The court agreed. By transferring the vast majority of her wealth — the palace and its contents, including the archives — to the foundation, the Duchess had exceeded the portion of her estate she was legally allowed to bequeath to non-heirs. The foundation was ordered to pay 27 million euros to the children as compensation. There was only one problem: The foundation had nowhere near that much money, and, as a national heritage site, none of it could be sold.

To further complicate matters, Leoncio wasn't satisfied with the ruling. He was after something more than money. As duke, he believed he should be responsible for the palace, the archives, and the family legacy. "Leoncio Alonso wasn't happy with this solution because it meant giving up his family's property, and he didn't want to be remembered as the first Duke of Medina Sidonia to allow this," Eduardo Ferreiro, Leoncio's lawyer, said at the time.

Leoncio appealed the ruling and won. But the victory proved pyrrhic. The higher court ruled that he and his siblings would become part owners of the palace and its treasures — though without any power over its administration, any right to distribute its contents, or any privilege to reside there. Liliane, the court added, could continue to live in the palace. The siblings were effectively owners of everything, and of nothing.

Infuriated, Leoncio decided to defy the court's ruling and take matters into his own hands. He moved into the palace, effectively becoming housemates with his mother's widow. "Cohabitation is uncomfortable," he told a reporter. "However, the house is big."

Things got messy, fast. A newspaper reported that Montserrat Viñamata, Leoncio's first wife, had become romantically involved with Liliane, whom she had known since their university days in Barcelona. Viñamata denied the rumor: "Whoever has insinuated this has done me a lot of damage," she told a local newspaper.

In 2023, Leoncio ratcheted up the dispute. He accused Liliane of taking money from his mother's estate. Liliane denied the charge, arguing that Leoncio was smearing her name in an effort to remove her as president of the foundation so he could take over in her place. Both of them declined requests to speak with me.

Earlier this year, a judge found Liliane guilty of misappropriating funds. She was sentenced to six months in prison and ordered to repay 280,000 euros. Her appeal is due to be heard by Spain's supreme court.

On a hot morning last summer, I sit down with Gabriel at a busy café terrace in Madrid. Dressed in navy blue shorts and a white polo shirt, collar up, he looks every inch the aristocrat. Slim, with wavy gray hair, he's the kind of well-read man who sprinkles his conversations with quotes from the French economist Thomas Piketty. He also takes after his mother. It's as if his obsession with her betrayal has so boiled within him that it now emanates from his very physicality. He has her rosy cheeks, her birdish eyes, her same stubborn drive.

Gabriel, divorced and childless, seems caught in a perpetual struggle to find his place in the world. He has a habit of talking in circles, though he always returns to the topic of how his family has been torn apart. "I've been at cafés with him," says a close family member, "and suddenly he'll just start talking to someone he barely knows about his quarrels with his mother."

His mother, he tells me, "never wanted to have any relationship with us. Above all, she saw us as a threat to the free disposal of her wealth." He claims he wants to mediate between his siblings and Liliane. "I see the foundation as running like a business," he says. "What interests me is that it's run well, not who runs it." But even those closest to him have trouble discerning his true intentions. "Gabriel's views on all this change — depending on how he wakes up in the morning," says his good friend and lawyer, Javier Timmermans.

Pilar, for her part, sees the family drama as integral to both brothers' emotional makeup. Gabriel "seems to be searching for headlines rather than solutions," she says, while Leoncio is "just interested in defending his claims" as the first-born son.

Pilar, a writer and a socialite, inherited her mother's flair for culture: One paper called her "possibly the most elegant woman in Spanish high society." If her brothers remain bent on getting justice, she's more interested in closure. "All that sensationalism doesn't matter," she says. "That might be fine for making a soap opera if they want, but solving the archives issue doesn't have to depend on that."

Pilar is the first to admit that she has good reason to seek a settlement. She has inherited her father's residence in central Spain, the González de Gregorio Palace, and she has taken to referring to it as her vampire because it sucks up all her money. "I would be lying if I said I didn't want to resolve this situation because I need to," she says.

Unfortunately for Pilar and her brothers, their father's estate is proving every bit as thorny as their mother's. A half-sister whom their father never recognized has come forward to demand a share of his estate, using the same provision of Spanish inheritance law that they themselves deployed against the foundation. In October, a court ordered Pilar and her brothers to pay the half-sister a sum of more than $1 million. Gabriel now fears they might be forced to auction off the rights to the archive to private bidders — a desperate measure to cover their spiraling debts. If that were to happen, the children would finally be separated from the archive, just as the Duchess had wanted.

A few months after meeting with Gabriel, I travel to Sanlúcar de Barrameda to see the Archive of Medina Sidonia for myself.

Walking through a labyrinth of narrow cobbled streets in the city center, I pass rows of simple white houses. Some of the facades are crumbling like stale bread; others are as pristine as a Hollywood smile. The whitewashed palace looms above the city, just as the family's thousand-year legacy has loomed over the children for their entire lives.

Past the sprawling Ambassador's Room where the Duke had filmed his triumphant return, I climb a flight of stairs to the attic. The Investigator's Room smells sweet and woody. A faint chill hangs in the air, and bright sunlight casts shadows across the high shelves lined with books. There I find Liliane, quietly tapping away on her laptop.

In an email to me, Liliane had accepted my request to visit the archive, but said she wouldn't comment on any legal matters, citing past experiences when she felt her words had been twisted. Her position on the archive, echoing that of the late Duchess, is that it belongs in public hands. "They are the only ones who, today, can guarantee its maintenance and preservation, as required in a technological world," she wrote, adding that "knowledge of the past is indispensable for moving forward in all aspects of human life."

True to her word, Liliane sits at the table beside me in silence while I study the archive. After several hours, she abruptly leaves without uttering a word.

I'm handed an accountant's ledger, which indexes the documents in the archive, the descriptions scribbled in the margins in the Duchess's spidery handwriting. I ask for a diary of the Almadraba — the famous local fishing season held every May for the past 3,000 years. The diary dates back to 1550, comprising a nearly indecipherable tabulation of the number of fish caught, and the money made in each village.

Sitting with the nearly 500-year-old document in the dim light of the library, I'm reminded that only a tiny part of the collection has been digitized. The history it contains is almost entirely physical. A fire, or a robbery, could cause the documents to disappear forever.

The most viable resolution is for either the state or a major cultural institution to step in and buy the estate from the siblings, turning it into a state-owned asset and ensuring the proper management and preservation of the archives. But that would cost a lot of money — and thanks to the Duchess, the government already has a role in the foundation's administration, providing resources and guidance. And so the feud rages on, with the children clinging to the legacy their mother never wanted them to have. Leoncio and Liliane continue to live in separate wings of the palace, each imprisoned by the limbo to which Spanish law, and their intertwined fate, have condemned them. Gabriel remains consumed by his vendetta against their mother, and Pilar remains locked in battle with the rest of the family. The Duchess, with her relentless dedication to the archive and her disregard for her own children, left them with an acrimonious and bitter future. They had succeeded at gaining part ownership of her estate. But what they'd won seems more like a share in her disdain.

Matthew Bremner is a writer based in Spain.