Director Matthew Vaughn has also cast Zoe Kravitz, Bill Milner and Morgan Lily as mutants
"Mad Men" star January Jones will play telepathic mutant Emma Frost in 20th Century Fox's "X-Men: First Class," an individual familiar with the project has confirmed to TheWrap.
That means Alice Eve, who was previously reported to be in negotiations for the role, will not be a part of the cast.
Additionally, Zoe Kravitz has been cast as Angel Salvadore (not the same character Ben Foster played in "X-Men: The Last Stand"), Bill Milner will play the really young version of Michael Fassbender's Magneto, and Morgan Lily will play Young Mystique.
Earlier in the week, Rose Byrne was reported to be playing Charles Xavier's (James McAvoy) love interest Moira MacTaggert, while Oliver Platt will play a mysterious figure named the Man in Black. Director Matthew Vaughn's "Kick-Ass" co-star Jason Flemyng will play Azazel, the father of Nightcrawler, though it's unclear if the latter actually will appear in the prequel.
Previously announced were Nicholas Hoult as Beast, Jennifer Lawrence as Mystique, Caleb Landry Jones as Banshee, Lucas Till as Havoc and Edi Gathegi as Darwin.
Kevin Bacon will play the villain, whose identity is being kept under wraps.
Jones recently got her first Emmy nomination for her performance on the third season of "Mad Men." She next plays Nicolas Cage and Liam Neeson's respective wives in the thrillers "The Hungry Rabbit Jumps" and "Unknown White Male."
Kravitz is now in theaters in Joel Schumacher's "Twelve." She next stars in "It's Kind of a Funny Story" and George Miller's "Mad Max" sequel, "Fury Road."
Milner previously starred in "Son of Rambow" and opposite Michael Caine in "Is Anybody There?"
Lily previously played John Cusack's and Radha Mitchell's daughter in "2012" and "Henry Poole Is Here," respectively. She recently appeared in Rob Reiner's "Flipped."