Bryan Singer insists X-Men: Days Of Future Past will be ''darker'' than the original trilogy and X-Men First Class.

In a Twitter chat the 48-year-old director said: ''Though there is a great deal of humour, the overall tone is a bit darker than previous films, particularly because of the stakes...''

Singer stepped in to direct Days Of Future Past after First Class director Matthew Vaughn pulled out of the project, but is no stranger to Marvel's X-Men franchise, as he has worked with it from the beginning, directing the original X-Men in 2000 and X2 in 2003.

He added: ''I was real comfortable with the original cast and knew the #FirstClass cast as a writer/producer but not yet as a director. With the exception of @NicholasHoult [Beast] of course - but they were all fantastic and made the experience fun.''

X-Men: Days of Future Past hits theatres on May 23, 2014.