Robert Downey Jr’s return to the Marvel Cinematic Universe (MCU) sent Avengers fans into meltdown – but the actor himself was left embracing his inner fanboy when two particular stars were cast in the new film.

Downey Jr is playing Avengers: Doomsday’s primary antagonist, Doctor Doom, in the film, which stars everyone from Chris Evans (Captain America) and Chris Hemsworth (Thor) to Pedro Pascal (Mr Fantastic) and Florence Pugh (Yelena Belova).

But for the former Iron Man actor, it was the return of the original X-Men that left him particularly excited, namely Rebecca Romijn and Kelsey Grammar, who are returning as Mystique and Beast.

“It was a big moment, you and Kelsey being back,” Downey Jr told Romijn at Comic-Con, where it was revealed that David Jonsson had been cast as the new Black Panther and that Ryan Gosling would be playing a new version of Ghost Rider.

Downey Jr said that all of the film’s cast, including Evans, Pascal, Paul Rudd (Ant-Man), David Harbour (Red Guardian), Letitia Wright (Shuri) and Lewis Pullman (Sentry), were overwhelmed to see them on set. “I have to say, we nerded out,” he told Entertainment Weekly.

He added that their presence “lit up this constellation of excitement”, calling their scenes “really incredible”.

Other X-Men stars returning in the film include Ian McKellen, Patrick Stewart, James Marsden, Alan Cumming and Channing Tatum.

Marvel fans got a better look at the forthcoming superhero film when an extended trailer premiered at Comic-Con.

The trailer emphasises Doctor Doom’s relationship with the Fantastic Four, making it clear that Pascal’s Mr Fantastic and the rest of the group have a troubled pre-existing relationship with the villain.

The footage was shown only to Hall H attendees at Comic-Con and is not yet available online. It follows the release of a first trailer last week, which fans branded “disappointing”.

Fans who have seen both appear to prefer the second, with many questioning why Marvel didn’t lead with it.

“OK, the second Doomsday trailer is so much better than the first,” wrote one person on X, with another echoing the same sentiment: “Why wasn’t this the first Doomsday trailer cause it’s way better than whatever that slop first trailer was.”

The forthcoming film, the first in a two-part Avengers finale, will feature almost every major character from the MCU. It’ll be released on 18 December – the same day as Dune: Part 3.