How the sequel to First Class became "Let's get the whole gang back."
It was a process. After we were done with First Class, Matthew Vaughn, myself, and Bryan [Singer] were all talking about what we would do for the sequel. Initially, we were just going to follow the First Class cast on the next adventure. Then we started talking about potentially using Ian McKellen and Patrick Stewart as bookends to the movie -- not as Days of Future Past, but just as sort of emotional bookends to the film. As we started developing that and as I started going through comics and thinking about a story that would be a cross-generational story, I came on Days of Future Past, which is one of my favorite runs in the comic. Then I pitched that, and Matthew loved the idea of it. Bryan was excited about it, and the studio got really excited. The thing that was daunting was getting this cast together -- schedule-wise, deal-wise, all of that, all of those logistics. But creatively everybody got really excited about it. That was probably spring of last year [2012]. Then I wrote the first draft of the script in the spring and the summer with Matthew primarily -- Vaughn was going to direct at the time. Then Matthew fell off the movie and Bryan came on from producing to directing, and we continued to work on the script in the fall and the beginning of this year. But it was just this process of, "How do we tell a story that feels like not just a repeat or a continuation, but an expansion of First Class?” We wanted to bring in the old Charles and Erik, and then from there it sort of evolved.
If the timelines of First Class and the original cast can be brought together in this film.
Well, it's interesting, because they still live in their coherent timelines. We have the characters from the original movies that take place in the timeline of X-Men 1 through 3, and then we have our X-Men: First Class characters that take place in the past. So given that we wanted to bridge those two casts, Days of Future Past is a comic that did it with time travel. I think initially we were all a little bit nervous about time travel because, you know, it's been done a lot in movies. It's really challenging as a writer to keep the logic of time travel straight and tell a story that isn't just servicing the sort of "A to B" butterfly effect of the time travel. We just didn't want it to be cheesy. The time travel element is something we talked about a lot -- setting up the rules of that time travel, setting up the stakes so that you have real stakes and goals in the future and the past story.
Something the movie obviously exploited. 
