James McAvoy has revealed X-Men: Days Of Future Past will be "the biggest, most epic" film of the franchise.
The Filth star will reprise his role as the young Charles Xavier in Bryan Singer's follow-up, which has finished filming in Montreal.
"Potentially it's going to be the biggest, most epic X-Men they've ever had," he told IGN.com. "I think it's the second biggest production Fox have ever embarked upon, behind Avatar. So they're definitely going for it."
The sequel to Matthew Vaughn's X-Men: First Class will jump between time periods, where the latest generation of mutants - James, Michael Fassbender, Jennifer Lawrence and Nicholas Hoult - will share screen time alongside the older cast including Hugh Jackman, Sir Patrick Stewart and Sir Ian McKellen.
"Weirdly the people that I spent the most time with acting-wise was not Michael this time, it was Hugh and Nick. I spent a hell of a lot of time with Nick," the Scottish star said.
"Getting to work with Hugh - who I christened Hugo Boss - was great. He's amazing. The guy's got grace coming out of every single pore."
He also got to act opposite Sir Patrick, who plays the older version of Professor X. "His last day was my first day and that was it. Then we were done. But we did crossover and we do get a scene together," he said.
James said having Bryan back at the helm has brought a "kind of reverence."
"Bryan's very protective of the series. He did create it. He did help form that environment that allowed subsequent superhero movies to exist and thrive. You know you're in good hands," he added.
X-Men: Days Of Future Past will be released in the UK on May 22, while Filth is out on October 4.