Once again it's being rumored that the X-Men will be coming back to Marvel.
Back last July saw a rumor hit that Fox and Marvel are planning an Avengers and X-Men move for 2020.
Now it's being said that following X-Men: Apocalypse, the X-Men will be rebooted within the Marvel Cinematic Universe, though Fox will still retain the rights.
The latest info comes from Comic Planet Culture For Life that also states X-Men: Apocalypse will be Bryan Singer's last X-Men movie.
It's also again said an announcement will be forthcoming; the first rumor stated an announcement about the X-Men and Marvel Avengers movie would be made at this year's Comic-Con, which follows the May premiere of X-Men: Apocalypse. Whether the announcement comes this year (if it happens) remains to be seen, but Disney could always announce the Avengers and X-Men event in 2017 at their D23 Expo which just moved to the month of July (the month Comic-Con is normally held).
Regarding any evidence that Fox is teaming with Marvel for Avengers and X-Men, back about two years ago Kevin Feige said "never say never" regarding Marvel teaming up with any of the other studios. Of course, now we know Marvel is working together with Sony on Spider-Man.
Notable X-Men producer Lauren Shuler Donner is also close to Marvel's Kevin Feige, as the two worked together, and previously offered she would "love it" if the characters worked together with an enthusiastic "yeah, absolutely," when questioned about a potential X-Men and Marvel crossover.
Possible further evidence may lie with the recent smash hit Deadpool movie, which features Marvel's Avengers hellicarrier in the climactic scene. The Hellicarrier in Deadpool was confirmed by the concept artist: "[I] was asked to redesign the helicarrier so it looked as different as possible from the one in The Avengers. And it had to look like it had been taken apart in some places," Emmanuel Shiu said.
It's also suggested the previous rift between Marvel Comics and Fox may be over as Marvel Comics is now producing various X-Men related comic books. Marvel Comics previously killed off various X-Men characters including Wolverine and blew up the cast of the Fantastic Four reboot in one of their books. There is also the fact Marvel and Fox are working together on the FX X-Men TV series Legion and Hellfire.
Regarding Fantastic Four, no rumors have suggested the property may be going back to Marvel, but if the X-Men rumors pan out, more than likely Kevin Feige and Marvel will be coming in to save the day for FF as well.