Robert Downey Jr. says original X-Men cast left him 'nerding out' on 'Avengers: Doomsday' set

Robert Downey Jr. has revealed that working alongside the original X-Men cast on Avengers: Doomsday was a surreal experience, admitting he "nerded out" when longtime franchise stars returned to reprise their iconic Marvel roles.

Speaking exclusively to Entertainment Weekly during San Diego Comic-Con, Downey Jr. said the arrival of actors including Kelsey Grammer and Rebecca Romijn created a special atmosphere on set, describing it as a moment that "lit up this constellation of excitement" among the cast. The actor now plays Doctor Doom after spending more than a decade portraying Tony Stark/Iron Man in the Marvel Cinematic Universe.

Downey said seeing the veteran X-Men stars reunite reminded everyone of the impact the original films had on the superhero genre. Grammer reprises his role as Beast, while Romijn returns as Mystique, joining fellow franchise veterans Patrick Stewart, Ian McKellen, James Marsden and Alan Cumming in the upcoming crossover event.

Grammer reflected on stepping back into Beast's shoes, saying the character's compassion and wisdom continue to resonate with him, while Romijn joked that advances in make-up technology have made becoming Mystique far less time-consuming than it was during the original trilogy.

Avengers: Doomsday will unite heroes from across the Marvel Cinematic Universe, including the Avengers, the Fantastic Four and the original X-Men, as they face Doctor Doom in one of Marvel Studios' biggest crossover films to date. The film is scheduled to arrive in cinemas on December 18, 2026.