Director Bryan Singer - who is returning to the franchise after directing the original 'X-Men' film in 2000 and its 2003 sequel 'X2' - confirmed the veteran actors will reprise their roles as Magneto and Professor X.
Bryan wrote on his twitter page: ''I'd like to officially welcome back James McAvoy, Jennifer Lawrence, Michael Fassbender, & Nicholas Hoult to #XMEN for #DaysOfFuturePast (sic).''
''Thrilled to announce @ianmckellen118 & @SirPatStew are joining the cast of #XMEN #DaysOfFuturePast #magneto #professorX More to come... (sic)''
'Days of Future Past', and its 2011 predecessor 'First Class', serve as prequels to the original trilogy, which also includes 2006's 'X-Men: The Last Stand'. James, 33, and Michael, 35, play younger versions of Professor X and Magneto in the films, respectively.
It appears the latest 'X-Men' will see plenty of time-bending to explain the co-existence of the returning elder actors - Ian, 73, and Patrick, 72 - and their younger incarnations.
Director Bryan Singer, 47, told Deadline: ''The movie is called 'X-Men: Days of Future Past', use your imagination.''
'X-Men: Days of Future Past' is due in cinemas in 2014.