Sir Ian McKellen thinks it is ''wonderful'' to be returning to the 'X-Men' franchise.

The veteran actor and his co-star Patrick Stewart were surprised to be asked to reprise their roles as Professor X and Magneto in forthcoming film 'X-Men: Days Of Future Past' because they thought they would be left to Michael Fassbender and James McAvoy, who played the younger versions of the characters in 'X-Men: First Class' and are also returning for the new movie.

Ian said: ''What a gas! I mean, Patrick Stewart and I have been have just been playing 'Waiting For Godot' throughout England and in the West End of London. So, we've stayed in touch.

''We can't believe it. I thought these were Fassbender and McAvoy's parts, but - no, no - we're back.

''We'll give them a run for their money. I mean, I haven't read the script, so I don't know how much we've got to do.

''But, to be back in that world, and for Bryan [Singer] to be doing it - with all the success he's had in the meantime - it's wonderful. Wonderful.''

And Ian was full of praise for Michael's portrayal of Magneto in 'X-Men: First Class'.

He added to the Huffington Post: ''I thought he was exactly that: first class. Excellent...

''I thought he was better than me. But, we weren't quite playing the same character because he was so much younger than me.''

'X-Men: Days Of Future Past' opens in cinemas 18 July 2014.