[Potential SPOILERS for X-Men: Dark Phoenix ahead.]
Rumor has it X-Men: Dark Phoenix will feature the death of a major character from the X-Men: First Class franchise. The upcoming film is being written and directed by Simon Kinberg, who previously adapted the famous Dark Phoenix comic book storyline (from Chris Claremont's Uncanny X-Men run) for the big screen with his script for 2006's X-Men: The Last Stand. This time around, however, Kinberg has far more creative control over the final product and isn't being forced to combine the Phoenix saga with the famous mutant cure storyline (from Joss Whedon's Astonishing X-Men run) into a single film, like what happened on The Last Stand.
Dark Phoenix picks up in the 1990s, continuing the trend of having each mainline installment in the X-Men movie franchise take place about a decade apart. That practice began with 2014's X-Men: Days of Future Past, which takes place ten years after the '60s-based First Class (the post-apocalyptic future scenes aside), and continued with the '80s-set X-Men: Apocalypse last year. First Class costars James McAvoy, Jennifer Lawrence, Michael Fassbender, and Nicholas Hoult are all returning for Dark Phoenix, along with Apocalypse costar Sophie Turner as Jean Grey. Dark Phoenix will build on the climax to Apocalypse in particular, where the young Jean unleashed her Phoenix powers in full for the first time, in order to destroy the eponymous mutant.
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According to THS' sources, Dark Phoenix will include a sequence where Jean uses her powers in full again, only for them to become too much for her to handle. This causes her to accidentally impale one of the main characters from First Class - Professor X (McAvoy), Mystique (Lawrence), Magneto (Fassbender), and Beast (Hoult) - in the process "unequivocally killing" them and further fueling Jean's descent into darkness.
It's certainly possible that Magneto will die at Jean's hands in Dark Phoenix, seeing as that would be a most unexpected development and could shake things up in the X-Men world something fierce for it. Such a move would only further muddle the messy continuity of the larger franchise, but at this stage most die-hard comic book fans seem to have made their peace with that lack of continuity (given that it seems to have benefitted the X-Men movies from a creative perspective) and/or just chalk it up to the alternate timeline that was seemingly created by the events of Days of Future Past.
Of course, if the idea is that this event is what pushes Jean completely over the edge (leading her to become the Dark Phoenix), then it might make sense for the person that she kills to be someone that she has more of a shared history with. Jean and McAvoy's finally-bald Professor X have a close relationship (as seen in Apocalypse), but his death at his student's hands might attract criticisms that Dark Phoenix is just recycling The Last Stand's storyline, which saw Patrick Stewart's Charles Xavier die at Jean's hands before being resurrected in a post-credits scene. Beast is also a possibility for related reasons, seeing as he too is one of Jean's trusted teachers at Xavier's School for Gifted Youngsters.
As for Mystique, she might be the strongest possibility of the four candidates listed here. Lawrence has said that she reprised her X-Men role in Dark Phoenix for the sake of the fans, and has made similar comments in the past signaling that she's not necessarily interested in hanging around as part of the X-Men franchise for as long as possible. Killing off Mystique in Dark Phoenix would provide Lawrence with an organic way to exit the franchise without having to return for the followup to the film that's already being planned (see also Olivia Munn's comments about Dark Phoenix being a "two-parter"). There's still a year to go before the film arrives, so any guess is fair game at this stage.
"Dark Phoenix" by Ian MacDonald, Sideshow Collectibles
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