Robert Downey Jr. may be returning to Marvel as Doctor Doom, but he reacted like a fan when members of the original X-Men movie cast joined Avengers: Doomsday.
During a post-Hall H interview at San Diego Comic-Con, Downey described the excitement generated by Rebecca Romijn and Kelsey Grammer, who are reprising their roles as Mystique and Beast.
The actors are part of a large crossover bringing Fox-era X-Men together with the Avengers, Fantastic Four and other Marvel characters. Downey said the returning mutants immediately energized the cast already assembled for the movie.
Marvel has confirmed multiple original X-Men stars for the film, but it has not disclosed how their characters enter the story or whether Mystique and Beast share scenes with Downey’s Victor von Doom.
Downey and His Costars ‘Nerded Out’ Over the X-Men
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Downey discussed the reunion while sitting with Romijn, Grammer and several other Doomsday cast members for an Entertainment Weekly interview. “It was a big moment, you and Kelsey being back,” Downey told Romijn. Referring to the other actors in the room, he added, “We nerded out.”
Chris Evans, Pedro Pascal, Paul Rudd, Letitia Wright, David Harbour and Lewis Pullman were among the costars participating in the interview. Downey said Romijn and Grammer’s presence “lit up this constellation of excitement” on the set.
He stopped short of revealing what Mystique and Beast do in the movie. Marvel has kept the central plot and most of the relationships between its different groups of heroes under wraps.
Rebecca Romijn’s Mystique Transformation Was Faster
Romijn first appeared as Mystique in 2000’s X-Men before returning for X2 and X-Men: The Last Stand. She also made a brief cameo in 2011’s X-Men: First Class.
Becoming the blue-skinned shapeshifter took considerably less time during Doomsday than it did for the original trilogy. Romijn joked that the new production was “no longer interested in waiting for actors to be processed.”
She nevertheless credited the lengthy transformation required by the earlier films with helping shape her performance. Spending hours in makeup placed her in the mindset needed to play a character whose anger was rooted in the treatment of mutants.
Kelsey Grammer Still Sees Nobility in Beast
Grammer debuted as Hank McCoy in 2006’s X-Men: The Last Stand. He later returned as Beast in the post-credits scene of 2023’s The Marvels, which placed Monica Rambeau in a reality inhabited by mutants.
Asked why he wanted to revisit the character, Grammer focused on Beast’s intelligence, compassion and moral principles. He said Hank carries a sense of nobility and a “deep respect for all life.”
Grammer also spoke about the hope represented by Marvel’s heroes, saying the characters can reflect a belief that goodness remains present even during difficult circumstances.
More Original X-Men Actors Are Returning
Romijn and Grammer will be joined by James Marsden as Cyclops, Patrick Stewart as Professor Charles Xavier, Ian McKellen as Magneto and Alan Cumming as Nightcrawler.
The returning actors connect Doomsday to the film series that began with X-Men in 2000, eight years before Downey’s first appearance as Tony Stark in Iron Man.
Downey is playing Victor von Doom rather than another version of Stark. Marvel Studios will release Avengers: Doomsday in theaters on December 18, 2026.