• "Wicked," the movie, is based on "Wicked," the hit 2003 Broadway musical.
• Cynthia Erivo and Ariana Grande play Elphaba and Glinda, roles originated by Idina Menzel and Kristin Chenoweth.
• Here's what you need to know about how the movie pays homage to the musical.

Warning: Spoilers ahead for "Wicked" the movie.

Jon M. Chu's "Wicked" film is a reboot of one of the longest-running Broadway shows of all time — and it pays its respects to that history through a long-rumored cameo.

"Wicked," the musical, is a loose adaptation of Gregory Maguire's novel that imagines a backstory for the Wicked Witch of the West from L. Frank Baum's "The Wonderful Wizard of Oz." The show premiered on Broadway in October 2003 starring Idina Menzel as Elphaba, the green-skinned woman who would become the Wicked Witch, and Kristin Chenoweth as Glinda, her roommate and future Good Witch.

Though "Wicked" has cycled through many Elphabas and Glindas over its extensive theatrical run, Menzel and Chenoweth remain iconic as members of the original cast. Now, they're passing the mantle to the film's Elphaba and Glinda — Cynthia Erivo and Ariana Grande.

Idina Menzel and Kristen Chenoweth have a significant cameo in the Emerald City

The cameo, which probably made Broadway fans squeal, happens once Elphaba and Glinda make their way to the Emerald City.

After sorcerer Madame Morrible recognizes Elphaba's immense magical talent, Elphaba enrolls at Shiz University to be her pupil. She ends up rooming with Glinda, her conceited classmate, and the two strike up a rivalry. Eventually, they become friends, and when Elphaba is summoned to meet with the Wizard in the Emerald City, she brings Glinda with her.

Once they reach the city, the pair take in the sights, including a play about the history of Oz and the Wizard. Menzel and Chenoweth appear as two of the show's principal players, and they're both credited on IMDb as "Wiz-O-Mania Super Star."

This isn't just a throwaway moment either. As far as cameo appearances go, this is a pretty meaty one: Menzel and Chenoweth have significant singing roles — Menzel even does her original "Defying Gravity" end riff.

The most satisfying part of their appearance, however, is their interaction with Grande and Erivo on-screen. There's one significant moment where Menzel and Erivo, and Chenoweth and Grande — the Elphabas and Glindas, respectively — stand face to face. Cheekily, Chenoweth places her mouth over Grande's mouth to prevent her from vocalizing and stealing the spotlight.

Both Menzel and Chenoweth have been champions of the film and supported it at its Los Angeles premiere. Both told Entertainment Tonight that they didn't think Erivo and Grande needed their advice — only their congratulations.

"Kristin and I are just so proud that we were a part of creating this beautiful legacy," Menzel said.

"You always hope they do a movie, especially when it's a juggernaut like this was, but you never know," Chenoweth said.

"Wicked" is now in theaters.