With Fox's X-Men: First Class set to begin filming next month in London, casting reports have kicked into high gear. In just the past 24 hours or so, we've seen conflicting claims about Aaron Johnson, unofficial announcements involving Nicholas Hoult and Caleb Landry Jones, and news of negotiations with Lucas Till.

Now comes word from Deadline that veteran actor Kevin Bacon has been offered the role of the mystery villain in the franchise reboot.

Although there's no hint as to who the film's antagonist is -- the synopsis merely refers to "the greatest threat the world has ever known" -- readers at Slashfilm quickly rallied around Mister Sinister, the long-lived geneticist who served as a major villain of Marvel's X-Men universe from the late '80s to the mid-'90s.

Bacon would join a rapidly growing cast that so far includes James McAvoy as Charles Xavier, Michael Fassbender as Erik Lensherr, Alice Eve as Emma Frost, Nicholas Hoult as Henry McCoy, Caleb Landry Jones as Sean Cassidy and, apparently, Lucas Till as Alex Summers. Aaron Johnson has been rumored as Scott Summers.

Directed by Matthew Vaughn, X-Men: First Class centers on the early friendship between Xavier and Lensherr, who work with other mutants to stop a global threat. In the process, a riff between them opens, beginning the war between Magneto's Brotherhood and Professor X's X-Men. The film opens on June 3, 2011.