With the X-Men movie franchise singing its swan song with the release of Dark Phoenix, a report has come out from THR that back in 2010 Fox toyed with the idea of making an X-Men vs. Fantastic Four movie.
According to THR’s “secret sources,” Fox considered a Civil War-esque superhero movie crossover that pitted the Children of the Atom against Marvel’s First Family. The battle was going to be ignited by Johnny Storm when he accidentally blew a hole in Manhattan after going supernova while trying to capture F4 villain Molecule Man, thus sparking the Superhero Registration Act in response to the devastation.
Source: IGN.com X-Men vs. Fantastic Four Movie Reportedly Almost Happened