In The Fantastic Four: First Steps, Latveria is referenced at least twice when we visit Earth-828's version of the United Nations. There's no mention of Doctor Doom, but the villain does appear in the movie's mid-credits scene.
During an interview with Phase Hero, filmmaker Matt Shakman confirmed that Robert Downey Jr. was the one wearing that green cloak for the sequence (which was shot on the set of Avengers: Doomsday by the Russo Brothers).
Now, The Cosmic Circus' Alex Perez is claiming that Downey's Victor Von Doom hails from Earth-828, the same reality as Marvel's First Family. He also says that Marvel Studios has "cooked" with the villain's MCU costume.
It makes sense for Doom to be from the same reality as the Fantastic Four because it gives them a built-in history with the villain, and means the team can deliver some handy exposition (Victor's backstory, for example) when they meet the Avengers.
Fans of Reed Richards' dynamic with Doom will likely also be pleased, as it means their history as bitter rivals remains. Marvel Studios hinted at that when the cast reveal ended with Pedro Pascal and Robert Downey Jr.'s chairs. This also goes some way in explaining why Victor would specifically target Earth-828's Franklin Richards.
Talking to Marvel.com, Marvel Studios President Kevin Feige addressed how the Fantastic Four will fit in with the Avengers and X-Men in Avengers: Doomsday.
"That’s always fun. The fun of an Avengers movie is introducing people to each other and seeing how very different personalities get along," he shared. "In the case of a movie that involves the threat of worlds literally colliding, it’s fun to see them visit each other’s homes."
"So with the Baxter Building set, let’s say it had four or five people in it at most in the Fantastic Four movie. And it’s got a heck of a lot more people in it [in Doomsday]. It’s a thrill to see that interaction," Feige continued. "And it’s surreal for me, who’s been around for 25 years."
Asked how it's felt to revisit the X-Men he originally helped bring to the screen in the early 2000s, the executive added, "It was another dream that we just didn’t think about for many years. Deadpool & Wolverine scratched the surface of that. And now, we’re really delving into it with Doomsday."
Avengers: Doomsday is set to be released on December 18, 2026, with Avengers: Secret Wars scheduled to arrive on December 17, 2027.