Updated October 15, 2015 a 1:15 p.m. ET: Multiple sources including Den of Geek are now reporting that 20th Century Fox did not relinquish film rights for Fantastic Four in order for these X-Men television deals with Marvel. Den of Geek, who posted the original rumor, has now stated that both 20th Century Fox and Marvel have said the original rumor was untrue.
Original Story: Did 20th Century Fox give the film rights to the Fantastic Four back to Marvel in exchange for the ability to expand its X-Men franchise to television? That's the rumor coming from Den of Geek.
Citing an unnamed source, Den of Geek reports that Marvel gave 20th Century Fox the rights to do the Legion (FX) and Hellfire (Fox) television series in exchange for the film rights to Fantastic Four. Both series were announced in somewhat surprise fashion Wednesday afternoon as being in development in partnerships between Fox and Marvel.
The source says that the rights reverting back to Marvel include ancillary characters such as Doctor Doom, Galactus and the Silver Surfer.
Den of Geek also claims a Fantastic Four reboot will be one of the three unnamed movies Marvel announced over the weekend to be released in 2020.
No other sources have come forward to verify the Den of Geek's report.
Interestingly, the deals for Legion and Hellfire were announced as a partnership between 20th Century Fox and Marvel Television, as opposed to Marvel Studios. The KevinFeige-controlled Marvel Studios reportedly recently left the control of the larger Marvel Entertainment unbrella, which still includes Marvel Television. If there's any veracity to the rumor, this would be an example of Marvel Studios and Marvel Entertainment/Television working closely with one another.