When does Legion return?

Dan Stevens starred as David Haller, a "mutant" diagnosed with schizophrenia at a young age. The series follows Haller as he tries to control his mutant powers and the sinister forces trying to control them while evading a government agency. The eight-episode first season of Legion aired from February to March 2017. A total of 27 episodes aired over three seasons.
David Haller was diagnosed with schizophrenia at a young age and has been a patient in various psychiatric hospitals since the diagnosis. He was committed to the latest facility by his adoptive sister, Amy Haller. Haller eventually discovers that his mind is infected by a parasitic mutant, another psychic named Amahl Farouk / Shadow King.