When Deadpool was released in 2016, it played fast and loose with continuity. Introducing a new version of Colossus—played by Stefan Kapičić in place of Daniel Cudmore—the movie was set in the X-Men Universe, or at least one very much like it.
The waters were muddied even further in Deadpool 2 when the prequel cast (who were then in the 80s or 90s, thanks to X-Men: Apocalypse and Dark Phoenix) made a cameo appearance in the present day. Even Deadpool & Wolverine seemed to further confuse matters by taking place after Logan, but bringing a Wolverine from another timeline into Wade Wilson's world.
Trying to make sense of 20th Century Fox's nonsensical X-Men continuity is nigh-on impossible. Fortunately for Marvel Studios, exploring the Multiverse means it's possible to visit similar worlds that are different where needed. That's why The Marvels featured a comic-accurate Beast who was still played by Kelsey Grammer.
Logan established that the X-Men no longer exist and that Professor X inadvertently killed them all. If that's the case in Deadpool's world, it suggests that Earth-10005 is not the same reality where Monica Rambeau has been left stranded.
Regardless, we know that a version of the X-Men will appear in Avengers: Doomsday, comprised of Professor X, Magneto, Cyclops, Mystique, Gambit, Nightcrawler, and Beast. For either financial or creative reasons, some heavy-hitters are notable by their absence, and we now have a possible explanation for why Jean Grey isn't there.
According to @MyTimeToShineH, Jean is dead in the world that Earth-616's heroes travel to, explaining why she isn't in Avengers: Doomsday. Whether she's still dead after the events of X2: X-Men United or something has happened since then isn't clear, but it's possible that she fell to the Doctor Doom-controlled Sentinels we've heard so much about.
When we return to the world of the X-Men, they may be nearing extinction, potentially explaining why Professor X and Magneto have seemingly pooled their resources (and giving Marvel Studios a convenient excuse for why every actor isn't returning).
We'll have to wait and see how things play out, but the next Avengers: Doomsday teaser trailer—which will revolve around the X-Men—could provide some answers.
Oh, and if you see this image floating around, we're hearing it's not real, but you never know...
Avengers: Doomsday officially stars Chris Hemsworth, Anthony Mackie, Winston Duke, Tom Hiddleston, Sebastian Stan, Letitia Wright, Paul Rudd, and Robert Downey Jr. Wyatt Russell, Simu Liu, Tenoch Huerta Mejia, Florence Pugh, Danny Ramirez, David Harbour, Hannah John-Kamen, and Lewis Pullman all make their Avengers franchise debuts in the movie.
The Fantastic Four: First Steps leads Pedro Pascal, Vanessa Kirby, Ebon Moss-Bachrach, and Joseph Quinn join them, as do X-Men franchise stars Kelsey Grammer, Patrick Stewart, Ian McKellen, Alan Cumming, Rebecca Romijn, James Marsden, with Deadpool & Wolverine's Channing Tatum. Chris Evans and India Rose Hemsworth are also confirmed to star.
The Russo Brothers direct Avengers: Doomsday from a screenplay by Stephen McFeely, with whom they previously collaborated on the Avengers and Captain America franchises. Loki and Doctor Strange in the Multiverse of Madness's Michael Waldron is also working on the script.
Avengers: Doomsday is set to be released on December 18, 2026, with Avengers: Secret Wars scheduled to arrive on December 17, 2027.