Jessica Chastain's mystery role in X-Men: Dark Phoenix may have finally been revealed. Far from playing an intergalactic warlord, she may actually be portraying the villainous Miss Sinister.

Back in August last year, Jessica Chastain confirmed that she was ing the X-Men franchise as she isn't Lilandra at all. Her mystery role is still one of Dark Phoenix's many mysteries, but a new rumor may indicate who she might actually be playing.

RELATED: Don’t Expect To See the X-Men in the MCU Until At Least 2021

The Tracking Board is reporting that Chastain is playing the part of Miss Sinister, a gender-swapped version of classic X-Men villain Mister Sinister. There's comic book precedent for the character; Sinister tends to switch his mind between bodies, and Miss Sinister is actually one comic book version of the evil scientist.

Miss Sinister X-Men

It's important to stress that this is only a rumor, and The Tracking Board doesn't give any hint as to how reliable they consider their source to be. At the same time, though, this is one rumor that would make a certain amount of sense. Sinister is strongly tied to Cyclops and Jean Grey in the original comics; he believed that their genetic code could truly unlock the unlimited potential of the mutant race. As such, Sinister intervened in Scott and Jean's lives time and again. When Cyclops was orphaned at an early age, Sinister actually had him sent to an orphanage he ran. When Scott's mutation began to trigger, it was Sinister who worked out that ruby quartz lenses reduced his headaches.

In the comics, Sinister was furious when Jean died in the Dark Phoenix Saga. He actually created a clone of Jean and manipulated events so she and Scott fell in love. Their son, Nathan Summers, became one of Sinister's most prized experiments; that son would ultimately become James Mangold took the film in a different direction.

If this Dark Phoenix rumor is true, it's an exciting one; Sinister is a classic X-Men villain, and Chastain's portrayal is sure to be tremendous. But right now, the rumor is unconfirmed, so it's best to take this news with a heavy grain of salt.

MORE: What's Going On With The X-Men Franchise?

Source: The Tracking Board