Kelsey Grammar, who played Beast in X-Men: The Last Stand, was one of the few original X-Men movie cast members who was not originally invited to reprise his role in X-Men: Days of Future Past.  But when Grammar got wind of the multi-generational nature of DOFP, he personally called director Bryan Singer and asked to play the Beast cameo.
 
As Grammar explained to Collider: "Actually I called Bryan.  I bumped into Hugh Jackman and he said, 'Oh you’re gonna be in another X-Men, mate!' and I said, 'No I'm not, I don't know anything about it.'  So I made a couple of inquiries, got a hold of the script, found out that it's primarily dealing with the past and that timeline I don't have a place in, but I saw that at the end there was this coda where he made an appearance.  I said, 'Listen, I really wanna be involved,' so Bryan arranged for it and I had a lovely time."
 
Grammar is eager to do another X-Men film, stating unequivocally: "I hope to do another.  I hope they find some way to come up with a new story that involves Beast in my timeline.  Though the next X-Men film, X-Men: Apocalypse is set in the 1980s and primarily involves the young X-Men of X-Men: First Class, word from writer Simon Kinberg is that there will some members of the original cast in Apocalypse, perhaps even Beast."