Fox reportedly commissioned a treatment from superstar comics writer Warren Ellis that would have seen the X-Men take on the Fantastic Four.

According to The Hollywood Reporterthis script was different from the one screenwriters Zack Stentz and Ashley Edward Miller wrote for the studio, details about which recently surfaced. Specifics about the Ellis treatment were not given.

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The Stentz and Miller script drew from Mark Millar and Steve McNiven's Civil War and would have set up Secret Invasion in its post-credits scene. Fox reportedly decided not to go forward with the film after the success of 2011's X-Men: First Class.

As the rights to Marvel heroes previously held by Fox now belong to Disney, the X-Men and Fantastic Four are fair game for future Marvel Studios films. However, Marvel Studios President Kevin Feige says fans shouldn't expect to see the X-Men in the Marvel Cinematic Universe for "a very long time."

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Directed and written by Simon Kinberg, Dark Phoenix is the last movie in Fox's X-Men franchise. The film stars James McAvoy as Professor X, Michael Fassbender as Magneto, Jennifer Lawrence as Mystique, Nicholas Hoult as Beast, Sophie Turner as Jean Grey, Tye Sheridan as Cyclops, Alexandra Shipp as Storm, Kodi Smit-McPhee as Nightcrawler, Evan Peters as Quicksilver and Jessica Chastain. The film is in theaters now.