(CNN) -- The cast of the upcoming film "X-Men: Days of Future Past" made a surprise appearance at Comic-Con this afternoon along with director Bryan Singer.
The cast members who appeared include those from the original "X-Men" movie franchise and those from 2011's X-Men reboot "X:Men: First Class." Jennifer Lawrence, Michael Fassbender, James McEvoy, Patrick Stewart, Halle Berry, Ian McKellen, Ellen Page, Peter Dinklage, Nicholas Hoult, Hugh Jackman, Evan Peters, Shawn Ashmore and Omar Sy assembled in Hall H to debut footage from the film.
Dinklage has been rumored to be playing the villain in the film since photos from the set leaked earlier this summer, but at first the "Game of Thrones" actor wouldn't confirm his role. "I'm playing Mystique," he joked. He later officially confirmed his participation by saying, "I get to play Bolivar Trask."
Singer directed 2000's "X-Men" and 2003's "X2," and produced 2009's "X-Men Origins: Wolverine." The director set up this new film in the series, which will be released in theaters on May 23, 2014, explaining the character of Wolverine (Jackman) will be the central figure bringing the story together. The upcoming "Wolverine" film out next week will act as a bridge for the character, Jackman said.
"The goal was to try and make a film that would bring this cast together by time travel or time displacement of some kind," Singer said. "Basically, the notion is that consciousness of Wolverine of the future is sent into his past self. And it was nice because Hugh was able to play both parts because the character of Wolverine is ageless. And it was great to be able to place him as a character in both these worlds. For me, it was great to reunite the old cast and get to work as a director with the new cast."
Singer also addressed rumors that this new film will rewrite the movie universe he's set up in prior films, specifically changing some of the events from "X2."
"Whenever you're going back in time -- and this is every bit as much a time travel movie as it is an X-Men movie -- there is those risks," Singer said. "I'm not the audience, I'm just the filmmaker, but I do believe in certain continuity that we'll maintain and some things we'll change. When you go back and mess about, things happen. So some of those rumors are probably somewhat true."
There will be some interaction between the older and younger versions of the characters, according to Singer. The director screened a reel of film footage that included a teaser of that.
"Wolverine is the journeyman," Singer said. "His interaction with the younger cast is primary. There is a moment, which you'll see in this reel, where these characters come face to face, older self with younger self. And we tried to do it in a unique way. It's been done before, but with my first opportunity to make a time travel film I want to create this set of rules and stay with them."
One of the big surprises is that Professor Charles Xavier (Stewart) is still alive after the events of 2006's "X-Men: The Last Stand." In that film, the character of Jean Grey killed Xavier -- mostly.
"My assumption was that it was going to be Ian and Halle and Hugh and everybody back, but it won't be me," Stewart said. "But something happened, which I'm not allowed to talk about -- am I?"
In my own mind I understand how Xavier is alive at the end of 'X-Men 3,'" Singer responded. "At the end of 'X-Men 3' after the credits when his consciousness is inside of this woman in a hospital and you take that and mix it with some powerful mutants -- mutants can do a lot of cool stuff -- you can imagine that anything is possible."
The film takes place during several time periods, including the 1970s, which allowed for some interesting costume choices beyond the X-Men suits.
"I personally love the moments when I get to wear the '70s clothes," said Lawrence, who (really) plays Mystique. "I really enjoy them because I love that time and I like wearing clothes when I can. Some of the Mystique stuff, some of the look is a little bit different. We're still using the same paint. When we left the (last) movie, she was mutant and proud. She was kind of struggling with the problem that a lot of normal human people struggle with, which is how they look. So she was very covered up in the first movie, but this time she is mutant and proud."
"It's a very collaborative thing," Fassbender added. "That's a thing that I've found as a whole: The clothes we wear, the Magneto outfit, being on set."
"The best thing about playing the older Magneto this time -- no helmet," McKellen said, telling Fassbender, "We'll talk about helmets later."
The cast members also discussed their ongoing friendships. One of the benefits of the film was bringing the original cast members back together and for Berry, who plays Storm, this film was a chance to reunite with old friends.
"We all love the films, but what's nice for me is that in the first movie we all became such good friends," Berry said. "And we really like each other and we like being around each other so to have a chance to do the work and hang out with the people we really respect, admire and like to be around is the joy of coming back to do these movies. The beauty is we pick up as if we just saw each other yesterday. I was really happy to see everybody and meet the new cast."