While the first three "X-Men" films were (relatively) contemporary, the Matthew Vaughn-directed "X-Men: First Class" turned back the clock to 1962 in order to explore the early days of Professor X, his friend-turned-nemesis Magneto and some of the younger mutants who would go on to form the X-Men.

With the upcoming sequel "X-Men: Days of Future Past," things could get a little funky. 

According to a casting call sheet obtained by Comic Book News, "most of the film" takes place in 1973. That's a full decade after the events in "First Class," which centered around the Cuban Missile Crisis. 

Returning director Bryan Singer has lined up a stellar cast for "Past," with veterans Hugh Jackman, Patrick Stewart and Ian McKellen rubbing shoulders with their "First Class" counterparts, including James McAvoy as a younger Xavier, Michael Fassbender as junior Magneto, Nicholas Hoult (Beast) and Jennifer Lawrence (Mystique).   

The most recent announcements also revealed the return of Shawn Ashmore as Iceman, Anna Paquin as Rogue, and Ellen Page as Kitty Pryde.


With the film taking place in two timelines  -- the 1973 "present" and a dystopian future era -- the returning "X-Men" cast members (Jackman, Stewart, McKellen, etc) will likely only be seen in scenes depicting the film's future. 

Before leaving the director's chair, Vaughn previously said he envisaged kicking off the sequel with the 1963 assassination of JFK, which seems much less likely now. However, '73 saw its share of significant shakeups,  including the end of U.S. involvement in the Viet Nam war; a crippling gas crisis; a war in Israel; and the aftermath of the Watergate scandal. 

The call sheet also notes that the Montreal shoot will last from April to August, which is a fairly long production schedule. 

"X-Men: Days of Future Past" will be released July 18, 2014.