In June, 20th Century Fox registered Days of Future Past as a possible title for the sequel to a prequel, and that served as a tip-off to the possible storyline.  The title refers to a two-issue tale by Chris Claremont and John Bryne  in 1981.  The story presents a scenario where Kitty Pryde arrives from a future in which the X-Men fail to stop a senatorial assassination, leading to an alternative timeline in which most of the X-Men are dead and mutants are living in internment camps.  Time travel shenanigans ensue.

The story could go well, especially given returning director Matthew Vaughn's stated desire to involve the Kennedy assassination in much the same way that a fictionalized certion of the Cuban Missile Crisis formed the backbone of X-Men: First Class.

We don't know if that specifically will be the case, but we do know that the sequel is definitely X-Men: Days of Future Past.

In an interview with IGN, Singer confirmed it, saying, " I can say it’s being written right now and it will start shooting in a few months.  It’s going to be very ambitious.  It’s called Days of Future Past and it deals with aspects of that comic but also some very new things.   I just don’t want to give any of it away.  Matthew Vaughn will be directing and I’m totally excited about it."

As for whether or not the time travel elements of the story will allow for cross pollination between the First Class continuity and that of the first three X-Men movies, Singer answered, "I think there’s a strong desire to broaden out the universe.  The X-Men universe on its own is every bit as big as the Marvel universe and I think it’s time to reach out and explore it and perhaps even bring some connectivity between the films, as Marvel’s done so well.  You may see some of that, I don’t know."

Simon Kinberg, who also contributed to the script for X-Men: The Last Stand and produced X-Men: First Class, is currently toiling away on the new screenplay for Vaughn and 20th Century Fox.  Vaughn and Kick-Ass writing partner Jane Goldman did quite a bit of heavy lifting on the script for First Class as it sprinted through production, so they might just revise Kinberg's work, too.

Production is tentatively scheduled to begin early next year.  Michael Fassbender and James McAvoy will reprise their respective roles as Magneto and Professor X, and will be joined once again by the likes of Jennifer Lawrence, Nicholas Hoult, January Jones, Zoe Kravitz, Caleb Landry-Jones, and Lucas Till.

Singer, meanwhile, is in post-production on his fantasy adventure movie Jack the Giant Killer for Warner Bros.

X-Men: Days of Future Past is set to hit theaters in just over two years, on July 18, 2014.