X-Men: Days of Future Past already promises to have a ridiculously star-studded cast, packed full of characters from both the present and future timelines of the X-Men Universe. Fans already know they can look forward to seeing young and old versions of Professor X (played by James McAvoy and Patrick Stewart respectively) as well as two versions of Magneto (Michael Fassbender and Ian Mckellen). Now there's news that there may be yet another character's future self will be making an appearance, if only as a cameo.

Showbiz Spy reports that Kelsey Grammer will briefly return to reprise is role as Hank McCoy, aka Beast, from X-Men: The Last Stand. The former Frasier star was brought on late to shoot the cameo for the upcoming film.

"Producers had the brilliant idea to bring back Kelsey for Days of Future Past," said an unidentified insider. "It wasn't hard to get him to sign on for a guest appearance. He jumped at the opportunity the second it was brought to his attention."

It seems as if the cameo was supposed to be kept under wraps, with Fox bringing Grammer on under the guise of another project.

"Kelsey's special cameo was secretly shot during post-production on the Fox lot under the impression that Kelsey would be on set to film a pilot for a different project," said the insider.

It is unknown at this point what role the future Beast will play in the movie, or whether or not he'll get to meet with his younger self, played by Nicholas Hoult.

Hoult revealed in an interview last month that Hank had developed a serum that would allow him to turn from man to beast, differing from the original character that was permanently in beast mode.

"What's happened up to this point is between the time of the last movie and this movie my character has created a serum which basically controls his mutation so his appearance is normal as long as he doesn't get worked up," said Hoult to Movieweb. "Any animal instinct or urges, that kind of brings him out. So yeah, he changes into Beast a few times throughout the story and they've done some great action sequences with him this time, particularly in the mansion flying around on these chandeliers and stuff."

X-Men: Days of Future Past hits theaters on May 23. Are you ready?