
There’s no doubt that Doctor Doom is the final boss of Avengers: Doomsday. Though we haven’t yet seen Robert Downey Jr’s take on the villain, The Fantastic Four: First Steps teased his arrival and the threat he’ll present to the eponymous team, and to Earth’s Mightiest Heroes. With Doomsday now in production, we can expect — or at least hope for — more details about the film, and how the Avengers will assemble this time around.
Thanks to Thunderbolts*, we know that there may be some infighting between the surviving members of the original team (led by Anthony Mackie’s Captain America) and the “New Avengers” formed by Valentina Allegra de Fontaine (Julia Louis Dreyfus). But Doomsday will also bring other super-teams into the mix, like the Fantastic Four, and we’ll even see the return of the X-Men from the Fox Universe. How the latter will fit into Doomsday has been a closely-guarded (well, not that closely-guarded) secret, but a new look behind the scenes might confirm one of the most prevalent theories about the conflict in the film.

Joe and Anthony Russo, the directors of Doomsday, recently shared a behind-the-scenes set photo via Instagram. At first glance, it doesn’t seem to reveal anything about the plot of the upcoming film. But the Russos’ caption — “Look hard...” — tells us that there may be a clue hiding in plain sight, and eagle-eyed fans might have already found it. The image seems to reveal the letter “A” on the far left, while the scaffolding on the far right reveals an “X.” By that logic, the Russos seem to be teasing a major clash between the Avengers and the X-Men: if these clues are accurate, then Doomsday could be a sneaky adaptation of the Avengers vs. X-Men event from the comics.
Fans have long anticipated a conflict between the Avengers and X-Men in Marvel’s Cinematic Universe, but with the latter team relegated to Fox’s Marvel Universe, a crossover was never feasible. Now that both teams are under one banner, it makes a lot of sense that the Russos would try to squeeze a reference to Avengers vs. X-Men into Doomsday. One X-Men actor has already seemingly confirmed a fight between the teams: Alan Cumming, who returns as his X2 character Nightcrawler in Doomsday, will reportedly trade blows with a member of the Fantastic Four.
“I’m sort of learning these fights and I’m like, ‘What? Who am I fighting with?’” the actor told Buzzfeed UK. “And they said, ‘You’re hitting Pedro Pascal against the head,’ or something.”

There is, of course, a chance that Cumming’s comments were a misdirect or embellishment. But the more we learn of Doomsday, the closer the story feels to a riff on Avengers vs. X-Men. It’ll be interesting to see how the Russos reconcile that conflict with the arrival of Doctor Doom: maybe he’s pulling strings from the shadows to pit these two teams against each other. Either way, our heroes will eventually have to join forces against him at some point. With so many characters to spotlight, it’s going to take a lot of work — but if anyone can do it, it’s the directors of Endgame.