The first tweet announced that James McAvoy (Professor X), Jennifer Lawrence (Mystique), Michael Fassbender (Magneto) and Nicholas Hoult (Beast) will be reprising their roles in the sequel to X-Men: First Class. It was always a given that McAvoy, Lawrence and Fassbender would be back, but it's nice to see Hoult made the cut as well. No word yet on any of the other surviving First Class actors making the sequel.
The next tweet is confirmation of what we were all hoping for. Ian McKellen and Patrick Stewart have also been officially cast in X-Men: Days of Future Past to play the more "mature" versions of Magneto and Professor X. This all but confirms the time travel suspicions about the film that make sense given the Days of Future Past comic storyline it is supposedly influenced by.
With McKellen and Stewart on the board, the door is wide open for other "modern" X-Men to appear in at least cameo form. The appearance of Professor X seems to indicate that any time travel will occur before the events of X-Men: The Last Stand, which means Jean Grey and Cyclops could show up as well.
The next rumor floating around is Halle Berry will, in fact, return and play storm in X-Men: Days of Future Past. With six cast members already announced via Twitter, expect Bryan Singer to take a little hiatus before revealing any more mutant names.
X-Men: Days of Future Past begins shooting early next year, after Jennifer Lawrence wraps up The Hunger Games: Catching Fire. It is scheduled to arrive in theaters on July 18, 2014.