Robert Downey Jr. Says Everyone "Freaked Out" with X-Men in 'Avengers: Doomsday'

The return of the original X-Men in Avengers: Doomsday didn’t just excite fans. Even Robert Downey Jr., who plays the villain Doctor Doom in Marvel’s new movie, celebrated the return of Kelsey Grammer and Rebecca Romijn to their roles as Beast and Mystique. In an interview with Entertainment Weekly after Marvel Studios’ panel at San Diego Comic-Con 2026, the actor commented on reuniting with the duo.

Downey Jr. called the veterans’ return "a huge moment" and revealed that the news thrilled the entire cast. "I have to say, we freaked out," he said. Without going into details about the characters’ role in the story, the actor said Grammer and Romijn’s presence "sparked a constellation of excitement" during filming: "It’s just incredible," he concluded.

Everything you need to know about Avengers: Doomsday

The villain of the story in the fifth Avengers movie will be Doctor Doom, played by Robert Downey Jr., the actor who portrayed the legendary Iron Man in the MCU’s Infinity Saga and now takes on the role of antagonist. Avengers: Doomsday will be directed by brothers Anthony and Joe Russo (Endgame), with a script by Michael Waldron (Loki) and Stephen McFreely (Endgame).

Marvel has already confirmed the main cast members for the new movie, in one of the biggest MCU star gatherings ever assembled. Returning from previous Avengers films are: Chris Evans as Steve Rogers, Chris Hemsworth as Thor, Anthony Mackie as Captain America, Sebastian Stan as the Winter Soldier, Paul Rudd as Ant-Man, Winston Duke as M'Baku, and Letitia Wright as Shuri/Black Panther.

Among characters introduced after Avengers: Endgame — in phases 4 and 5 of the MCU — we have Simu Liu as Shang-Chi, Danny Ramirez as Falcon, the entire new Fantastic Four (Pedro Pascal as Mister Fantastic, Vanessa Kirby as Invisible Woman, Joseph Quinn as Human Torch, and Ebon Moss-Bachrach as the Thing), almost the entire cast of Thunderbolts* (Florence Pugh as Yelena, Wyatt Russell as U.S. Agent, David Harbour as Red Guardian, Hannah John-Kamen as Ghost, and Lewis Pullman as Bob, the Sentry), and Tenoch Huerta as Namor.

In a livestream announcing the cast, there was also the movie’s biggest surprise so far: the return of the classic X-Men from the old Fox films, including Patrick Stewart as Professor X, Ian McKellen as Magneto, James Marsden as Cyclops, Alan Cumming as Nightcrawler, Kelsey Grammer as Beast, Rebecca Romijn as Mystique, and, introduced in Deadpool & Wolverine, Channing Tatum as Gambit.

Avengers: Doctor Doom premieres on December 18, 2026.