• "Captain America: Brave New World" includes a cameo from Sebastian Stan, who reprises his role as Bucky.
• Bucky gives Sam Wilson a pep talk and assures him that he's worthy of being Captain America.
• The scene also teases Stan's return as Bucky in "Thunderbolts*."

Warning: Major spoilers ahead for "Captain America: Brave New World."

"Captain America: Brave New World" is filled with heroic moments from Anthony Mackie's titular superhero, Harrison Ford transforming into the comic book character Red Hulk, and a surprise cameo from a fan-favorite Marvel character.

The fourth "Captain America" movie follows Mackie's Sam Wilson after he inherited Steve Rogers' (Chris Evans) shield and the title of Captain America in "Avengers: Endgame."

In Sam's first solo outing as Captain America, the everyman character struggles with the pressure and responsibility of saving the world despite not having superpowers or special abilities. But a visit from an old friend reassures him that he was chosen as Steve's successor for a reason.

Here's everything to know about the movie's standout cameo.

Sebastian Stan returns as Bucky Barnes to give Sam Wilson a much-needed pep talk

Sebastian Stan was last seen as Bucky Barnes in the 2021 Disney+ miniseries "The Falcon and the Winter Soldier," which costarred Mackie.

In "Brave New World," Sam successfully stops rogue US fighter pilots from attacking a Japanese fleet. But in the process, his sidekick Joaquin Torres/The Falcon (Danny Ramirez) gets injured mid-flight and crashes into the Indian Ocean. After being rescued, Joaquin is immediately taken to the ER.

Sam, feeling guilty for what happened, watches through a window as doctors attend to Joaquin's extreme injuries. Then, Bucky arrives in a suit and stands next to Sam.

"Hate to admit it, but I'm glad you're here," Sam says, as the two hug.

After Bucky tells Sam that Joaquin's accident isn't his fault, Sam replies, "It makes me think of Steve."

The two talk about how Steve successfully stopped two alien invasions, and Sam, by comparison, feels unqualified and unworthy of being Cap.

"What made me think I could follow that?" Sam says.

Sam adds that he should have taken the super-soldier serum like Steve and Bucky did because all of this is bigger than him and his human limitations.

"Steve made a mistake," Sam says.

"You're a human being," Bucky replies "You do your best. Steve gave them something to believe in. You give them something to aspire to."

To emphasize his point further, Bucky concludes, "He gave you that shield not because you're the strongest, but because you're you."

"Did your speechwriters help you with that?" Sam jokes.

Then, Bucky leaves for a political campaign obligation.

Once he exits, Ruth Bat-Seraph (Shira Haas), the security advisor to US President Thaddeus Ross (Ford), refers to Bucky as "future congressman James Buchanan Barnes."

Stan's cameo sets up his appearance in the next Marvel movie, 'Thunderbolts*'

Stan will return as Bucky in the film "Thunderbolts*," set for release in theaters on May 2.

Eagle-eyed fans already picked up on Bucky seemingly wearing a US Congress pin in the most recent trailer for "Thunderbolts.*" His cameo in "Brave New World" tees up this surprising pivot from an assassin to a congressman.

"Thunderbolts*" centers on Bucky and a group of misfit Marvel characters who team up to stop a mysterious new threat.

The ragtag team of unlikely world-savers consists of Yelena Belova (Florence Pugh), Alexei Shostakov/Red Guardian (David Harbour), Ava Starr/Ghost (Hannah John-Kamen), John Walker/US Agent (Wyatt Russell), and Antonia Dreykov/Taskmaster (Olga Kurylenko). The movie also stars Julia Louis-Dreyfus as the enigmatic Valentina Allegra de Fontaine and MCU newcomer Lewis Pullman as Bob/Sentry.

"Captain America: Brave New World" is now playing in theaters.

• "Captain America: Brave New World" has one post-credits scene.
• The scene features Sam Wilson/Captain America and Samuel Sterns/The Leader.
• Their conversation alludes to the next big Avengers team-up.

Warning: Major spoilers ahead for "Captain America: Brave New World."

If you head to the theater to watch "Captain America: Brave New World" this weekend, you may want to stick around until the very end.

The fourth "Captain America" movie stars Anthony Mackie as Sam Wilson/Captain America after Steve Rogers (Chris Evans) passed the shield to him in "Avengers: Endgame."

Sam accepted the position and got a Cap suit of his own in the 2021 Disney+ miniseries "The Falcon and the Winter Soldier." But in "Brave New World," Sam is still grappling with his role as a hero without superpowers — while also ending up in the crosshairs of an international incident.

After all the credits roll, the movie concludes with a scene that teases action to come in the Marvel Cinematic Universe (MCU).

Sam Wilson pays the villain, Samuel Sterns, a visit at the Raft

In the MCU, the Raft is a maximum security prison where super-powered or enhanced individuals are incarcerated. Thaddeus Ross (then played by late actor William Hurt) previously locked up Sam and some of the Avengers at the Raft after the events of "Captain America: Civil War."

But by the end of "Brave New World," the tables are turned, and Ross (now played by Harrison Ford) is imprisoned inside the Raft after he transforms into Red Hulk and causes destruction in Washington, D.C.

Samuel Sterns/the Leader (Tim Blake Nelson), the antagonist who orchestrated a string of events to destroy Ross' legacy, is also sent to the Raft for his actions.

In the end-credits scene, Sam visits Sterns at the prison and tells the brainiac character that he's not in the mood for his jokes.

"You killed a lot of good men trying to get your revenge," Sam tells him. "Trust me, we don't share the same sense of humor."

Sterns, who can predict what will happen by calculating statistical odds, then shares a warning for the hero.

"We share the same world, don't we? This world you would die to save, it's coming," Sterns says. "I've seen it in the probabilities, seen it plain as day — all you heroes protecting this world. You think you're the only ones? You think this is the only world? We'll see what happens when you have to protect this place from the others."

The scene ends with text that reads: "Captain America will return."

The next Avengers team-up is coming

Near the end of "Brave New World," Sam tells Joaquin Torres (Danny Ramirez), his mentee and the new Falcon, that Ross was right about one thing: the world needs the Avengers. The end-credits scene reiterates this point without offering much else.

Plus, Sterns' tease about the next superhero team-up isn't brand-new information to fans.

Since "Endgame," the MCU has been expanding the storylines for the more recent additions to the Avengers lineup and introducing new characters to rebuild the team in the absence of people like Tony Stark/Iron Man (Robert Downey Jr.), Steve Rogers, and Natasha Romanoff/Black Widow (Scarlett Johansson).

It'll culminate in the next two "Avengers" movies, which are part of the MCU's Multiverse Saga: "Avengers: Doomsday," set for release on May 1, 2026, and "Avengers: Secret Wars," scheduled for May 7, 2027. Both will be codirected by sibling duo Joe and Anthony Russo, who directed the last two "Avengers" movies.

Details about the "Doomsday" plot are unknown, but the ensemble film will star Mackie, Downey Jr. as the villainous Doctor Doom, maybe (or maybe not) Benedict Cumberbatch as Stephen Strange/Doctor Strange, and the cast of the upcoming "Fantastic Four" reboot.

Evans will reportedly appear in "Doomsday," though he denied his involvement in a recent interview with Esquire.

"Captain America: Brave New World" is now playing in theaters.