While Bryan Singer's X-Men: Apocalypse wasn't the end of 20th Century Fox's X-Men franchise, it turns out the 2016 movie was supposed to directly set up Channing Tatum's Gambit movie.
Speaking during a recent IGN quarantine watch party for X-Men: Apocalypse, writer/director Simon Kinberg confirmed the tease for Mister Sinister was going to set up Gambit. "We had a tease of it at the end of Apocalypse. The Essex Corp is something that you see in a tag at the end of Apocalypse," Kinberg explained. "We had talked about doing something with him, and I won't get into the specifics of it since it's no longer a 20th Century Fox property and now it's part of the MCU. I have no idea what the plan is. But Mister Sinister was going to be part of the Gambit movie starring Channing Tatum."
Following the success of X-Men: Days of Future Past, Fox moved ahead with Apocalypse and brought back the characters from the "reboot" timeline that started with X-Men: First Class. As well as introducing Alexandra Shipp's Storm, Tye Sheridan's Cyclops and Sophie Turner's Jean Grey, Apocalypse also had a major cameo from Hugh Jackman as Wolverine. The movie ended with a return to the Alkali Lake facility when a group of men collected an X-ray and blood sample for "Weapon X" on behalf of the Essex Corporation.
It's interesting to note the Mister Sinister tease was planned to tie into Gambit and not the next main X-Men movie. Kinberg didn't reveal why the plans were changed or how Mister Sinister would've evolved to fit into Gambit. The long-awaited Gambit appears to be one of the many casualties of Disney's acquisition of 20th Century Fox. Although Gambit went through several directors and phases, Kinberg was spurred on by the success of Logan and wanted to capture the movie's Western aesthetic. After Gore Verbinski left over creative differences and Disney bought the franchise, producer Lauren Shuler Donner eventually confirmed Gambit was placed on indefinite hold alongside several other projects.
This isn't the first time Mister Sinister was supposed to rear his head in the world of the X-Men. Josh Boone confirmed Disney cut a post-credits scene from The New Mutants that introduced Jon Hamm as Mister Sinister and set up a possible sequel. Despite Gambit's cancelation, Tatum has previously expressed interest in directing as well as leading the movie. Ultimately, there's a question mark hanging over mutants in the Marvel Cinematic Universe and whether any of Fox's X-Men properties will make the move to the House of Mouse.
Dark Phoenix followed X-Men: Apocalypse and was the last of Fox's X-Men films to arrive in theaters before the company's eventual merger with Disney.