"X-Men: Days of Future Past" is a serious movie.

That much has been made clear from the trailers for the Fox flick, providing viewers with glimpses of giant killer robots and a dystopian future. But regardless of the material's intensity, the people behind the film kept the mood light on the set -- and at the Ritz Carlton in New York City where cast, producers and crew convened for a press conference on the morning of the film's premiere. In attendance were stars Hugh Jackman, Patrick Stewart, Michael Fassbender, James McAvoy, Ellen Page and Peter Dinklage, as well as screenwriter and producer Simon Kinberg, and producers Hutch Parker and Lauren Shuler-Donner.

"The whole time, as intense as the material was, it was unbelievable," said Jackman, who returns as Wolverine, the character that bridges the film's future and past segments. "I'm probably uniquely qualified to say, from working with everyone, that being on the set throughout the whole thing was a joy." The cast's tight bond has been evident ever since they first came together in 2000's "X-Men," and this assemblage of actors has only grown more affable with age and every new addition.

WATCH: The "X-Men: Days of Future Past" Easter Egg in "Amazing Spider-Man 2"

The "X-Men: First Class" additions, McAvoy and Fassbender, now get to headline a film with the actors that originated the roles of Professor Xavier and Magneto -- Stewart and the absent Ian McKellen. And, as seen in the trailers, McAvoy even got to perform a scene with Stewart, with the two Xaviers acting face to face on an intimate, no-frills set. "It was, in a sense, a no-brainer how that [scene] was staged," explained senior Xavier, Stewart. "If it had been in a set where we could have gone for cocktails, opened the window, had a cigarette, [it would have been] a very different kind of scene. I'm not quite sure how it came about, that we were nose to nose like that, but I can't now think of any other possible way of making the scene work, because you are looking into the eyes of yourself."

"I've been a fan of Patrick for [many] years," said McAvoy of his fellow professor. "I watched him for seven years in 'Star Trek' and way back to 'Dune.' So getting to come and do my version of a character that he's been in charge of for fourteen years, and at his face, [it] was quite nerve-wracking."

Fassbender joked that the two Xaviers got a scene together instead of the two Magnetos thanks to a lost bet. "We flipped a coin, and James and Patrick won the coin toss," the younger mutant master of magnetism teased dryly. The young Magneto didn't even get to meet Ian McKellen until last year's Comic-Con International. "We sort of kept missing each other," Fassbender explained. But the actor did not let those missed connections deter him from getting into character. "For this one, I spent more time [watching] this thing on YouTube, which was Ian McKellen in the '70s, giving an RSC workshop about 'MacBeth,' and that ran for about ten minutes, so I was just playing that, over and over again."

While fans are eager to see old favorites like Storm and Kitty Pryde mix it up with the newer characters introduced in "First Class," there's still a bit of trepidation as to just how one film can juggle this many characters. As the screenwriter, Kinberg understood those fears and had to devise a way to overcome them.

"I don't think I've ever seen a movie with this many lead roles," he said. "That was the biggest challenge, was just keeping all of the characters straight in their own stories, and making sure that everybody had their own emotional arc over the span of the movie... I had colored notecards on the wall, different colors for each character... But that kept it straight for me, because I could look at the board and see each of their stories broken up separately."

Fan favorite actor Peter Dinklage joins the X-franchise as Bolivar Trask, the scientific genius behind the mutant-hunting Sentinels -- but don't call him the bad guy just yet. "Define villain," the actor responded when asked about his trouble-making character. Dinklage explained that questioning whether or not Trask is really the bad guy was "more like a highfalutin actor thing of not judging your character, seeing them as a villain." Dinklage clarified his character's motives, saying, "He really believes he's doing the right thing. He wants to save humankind, worldwide."

Like its predecessor, the '60s-flavored "First Class," "Days of Future Past" pulls double duty as both a period piece and a super hero film. This time, however, the film dives into the '70s, drawing on everything from the era's political climate to the hairstyles -- much to Wolverine's delight. "I don't think Wolverine ever wanted to leave the '70s," Jackman exlaimed. "The hair, the muttonchops, everything. The clothes, the cars -- I think the moment that Tears For Fears, Flock of Seagulls, Wham!, Duran Duran came along, Wolverine was like, 'I'm out!'"

"There's so much about the script reflecting [the past films and] calling [elements] back for fans," Jackman said, explaining how this film is a bit of a love letter to the audiences that have kept the hit movie franchise going. "There's so many great surprises in there for fans of the X-Men -- not only comics but the film series -- and yet you still make the film feel like not just a celebration, but a fresh beginning. I feel like, watching this movie, we could start again, and it feels like an opening."

Stewart shared a similar sentiment, making a pitch to longtime producer Shuler-Donner. "It made me feel that I really would like to go back, Lauren, and shoot all the other movies again, now that I know exactly where I came from and what I was. I could get so much more James McAvoy into that role."

"I think everybody needs a little James McAvoy in them," the young Xavier quipped. However much he was joking, though, the seriously hopes the "X-Men" franchise still continues to want more McAvoy. When asked if this would be both his and Fassbender's final X-Film, McAvoy said "We love you guys!" declaring his affection for the cast and -- especially -- the producers.

Stepping up for his younger self, Stewart said he hopes to see the franchise's new iteration continue on. "Where we leave James in this story, we are waiting to see the transition, the reformation of this character happen. That's a movie I would pay money to see."