FX CEO John Landgraf said that "Legion" takes place in a parallel universe in which the public is unaware of mutants, reported Entertainment Weekly.
"The US government is in the early days of being aware of mutants, but the public is not," Landgraf said.
He suggested the parallel universes would make it impossible for current X-Men characters to appear, but after "X-Men: Days of Future Past", we know it's possible, right?
"Legion" is the story of David Haller, a schizophrenic young man who discovers that the voices in his head could actually be a symptom of superpowers, and not psychosis.