Sir Ian McKellen and Michael Fassbender didn't collaborate on their portrayals of Magneto in 'X-Men: Days of Future Past'.

McKellen will play the older version of the comic book villain in next year's summer blockbuster, while Fassbender will play the younger version, but the two stars opted not to influence the other's portrayal of the complex character.

Veteran actor McKellen said: ''I think he [Fassbender] made it clear that he wanted to be his own Magneto, and that suits the nature of the story and his part in it.

''[Director] Bryan Singer clearly doesn't mind that we, Fassbender and I, don't look much like each other, although they have put out a poster where our faces are blended and you do a double take and think, 'Oh my goodness, I didn't know I was that good looking', and then realise the bit that's good looking is not me, but Fassbender!''

Fassbender and McKellen won't share scenes in the time-travelling flick, but their co-stars Sir Patrick Stewart and James McAvoy will come face-to-face as the younger and older versions of Professor X, aka Charles Xavier.

Stewart admits it was a ''happy charm'' about the exciting scene.

He explained to the Wall Street Journal: ''There was a certain happy charm about it, in that, when we shot that scene it was James' first day of work on the movie, and it was my last day. So I was saying goodbye to 'X-Men' and he was saying hello.

''James has seen everything that we've done [in the earlier 'X-Men' films]. I've seen everything he has done. He is illustrating a time in Charles Xavier's life which was very different from the time that I've been inhabiting in the previous three movies, and we just let that play out.''

'X-Men: Days of Future Past' will hit the big screen in May 2014.