The Russo Brothers were already working on a new project with Robert Downey Jr. when they got the call to return for Avengers: Doomsday.

The audience at San Diego Comic-Con got a huge surprise when not only was it revealed that Joe and Anthony Russo would direct Avengers: Doomsday (and Avengers: Secret Wars) but that Robert Downey Jr. would be playing Doctor Doom. However, the Russo brothers told GamesRadar+ that they had already been working on another project with Downey Jr. before they got the call.

“We’re all very close,” Joe Russo said. “We had been working on another project before Marvel approached all of us – so we’re working on another project with Robert – and there was a story that evolved through conversations that we got very excited about. Because it’s always got to be the story.” It’s unclear what this secret project was, but perhaps they’ll return to it once they wrap up Avengers: Doomsday and Avengers: Secret Wars.

As for Avengers: Doomsday, all Joe Russo would say is that we can expect something “really explosive” with the movie. “Why would we come back if we didn’t feel like we had a story that had that possibility of being on an equal footing with Infinity War and Endgame unless there’s a kernel there for an idea that’s really explosive?“

Downey Jr. has previously explained that the Doctor Doom train started rolling about a year ago when Marvel Studios president Kevin Feige sat down with the actor and his wife and producing partner, Susan Downey. “Probably a year ago, because Feige and I have kept in touch,” Downey said. “We’re pals. Favreau and Feige and I have kept in touch. I’m close with the Russo brothers. We have other business we’re doing. So there’s this little group of fellow travelers, and I had this instinct that I wanted to go to Bob Iger. And I had an idea, outside of the cinematic universe, for how I could be of service to what’s going on in the parks and all their location-based energy. And Susan and I were sitting down with Feige at one point, and he said, ‘It just keeps occurring to me that, if you were to come back…’ And Susan was like, ‘Wait, wait, come back as what?’“

Downey continued, “And then we both realized, over time, that it was another thing that just disproves any doubt anyone could ever have about that guy. [He’s] a very sophisticated, creative thinker about, ‘How can we not go backwards? How can we not disappoint expectations? How can we continue to to beat expectations?’ And he brought up Victor von Doom, and I looked into [the] character, and I was like, ‘Wow.’ And later on, he goes, ‘Let’s get Victor von Doom right. Let’s get that right.’“

Avengers: Doomsday is slated for a May 1, 2026 release, followed by Avengers: Secret Wars on May 7, 2027.