The classic Fox X-Men are returning in Avengers: Doomsday, and I've got a really bad feeling about this

Marvel Studios' first wave of cast reveals for Avengers: Doomsday included several of the OG Fox X-Men, including Kelsey Grammar as Beast, James Marsden as Cyclops, Rebecca Romijn as Mystique, Alan Cumming as Nightcrawler, Patrick Stewart as Professor X, and even Ian McKellen as Magneto, along with the addition of Channing Tatum's Gambit.

As much as that's a pleasant surprise - especially Ian McKellen getting his victory lap as Magneto alongside Patrick Stewart's Charles Xavier - it's got me fearful that we're being set up for a gut-wrenching Avengers: Doomsday rug-pull in which we'll be forced to watch an entire universe of heroes die before our very eyes.

But which one? Is Marvel setting up the death of the Fox X-Men Universe, or the MCU? It's not the wildest question to ask, and the answer could wind up shocking viewers to the core.

Let's look at the established facts from the MCU so far, along with the comic book precedent that has me shaking in my boots that the Marvel Cinematic Universe as we know it could be about to meet its final doom.

Given the inclusion of Kelsey Grammar's Beast and Patrick Stewart's Professor X, it seems pretty safe to assume they'll be picking up from the post-credits scene of The Marvels, in which the Monica Rambeau of the 616 Universe wakes up in an alternate reality populated by several classic X-Men.

It's also all but guaranteed that Avengers: Doomsday will center on an Incursion - a collision between two realities that leaves one of them destroyed. An Incursion between the 616 and another reality was teased way back in Doctor Strange in the Multiverse of Madness, with further mentions coming as recently as the post-credits stinger of Captain America: Brave New World, in which Samuel Sterns cryptically warns Sam Wilson that there is another challenge ahead, that may involve fighting people from another world.

"We share the same world don't we, this world that you will die to save. It is coming. I've seen it in in the probabilities, plain as day," he states. "All you heroes protecting this world, you think you are the only ones? You think this is the only world? We'll see what happens when you have to protect this place from the others."

This leads to the likely conclusion that, whatever happens when they come together, the MCU and the universe of the classic Fox X-Men are about to collide. There are even clues that the story will be less of a team-up, and more of a winner-takes-all Avengers Vs. X-Men brawl - something that has happened plenty of times in comic books, especially 2012's Avengers Vs. X-Men event comic - with the fate of their respective realities hanging in the balance.

It may be easy to assume that the 616 will come out on top, but with directors Joe and Anthony Russo calling Avengers: Doomsday and its sequel Avengers: Secret Wars a "new beginning" for the MCU, it's all too possible that the world we've been watching develop since 2008 will truly end in 2026, only to be relaunched by the end of Secret Wars. That would put the launch of a nu-MCU right around 2028, the 20th anniversary of the release of Iron Man, which put the MCU in motion.

If that seems far-fetched, the fact that the directors are invoking the comic book event Secret Wars for what will be the sixth Avengers film could lend even more credence to the idea that not just one but both realities may wind up on the chopping block, reduced to nothingness in the cosmic waves of time.

In 2014/15's Secret Wars, which took its title from the original 1985 Secret Wars comic event, a series of Incursions leads to basically the entire Marvel Multiverse being destroyed, with only Doctor Doom himself able to preserve reality itself from collapsing.

Pulling together shards of destroyed worlds from across the Multiverse, Doom becomes the absolute master of a hodgepodge reality called Battleworld, which exists in a tenuous feudal system under Doom's iron fist.

Only Reed Richards, Miles Morales' Spider-Man, and a few others remain outside Doom's control, eventually assembling a resistance against Doom. It all ends in a clash between Richards and Doom, with Mister Fantastic finally coming out the winner against his arch-nemesis.

After Secret Wars, Reed Richards leads his Future Foundation in rebuilding the lost Multiverse, with the original 616 being mostly restored - albeit with a few key changes that brought characters from alt-realities, such as Miles Morales, into the core Marvel Universe on a permanent basis.

What all this means is, in the question of whether the 616 or the Fox X-Men universe could survive their almost certain upcoming Incursion, the answer may in fact be that both universes will die right before our eyes - a tragic escalation of Thanos wiping out just half a universe in Avengers: Infinity War.

I'm certainly preparing my tissues, and I'm also setting my expectations that whatever comes out the other side, when the MCU is inevitably restored, it won't be quite exactly the world we've lived in for almost 20 years now.

Avengers: Doomsday is set to hit theaters on May 1, 2026. For more, check out our list of all the upcoming Marvel movies and shows you need to know about.