Singer, who directed the original X-Men in 2000 and 2003's X2, took to the social networking website last week (28Nov12) and revealed to fans that McKellen and Sir Patrick Stewart would join X-Men: First Class stars Michael Fassbender and James McAvoy in his new 2014 blockbuster X-Men: Days of Future Past.
He tweeted, "Thrilled to announce @ianmckellen118 & @SirPatStew are joining the cast of #XMEN #DaysOfFuturePast."
However, McKellen admits he was taken by surprise by the declaration - because he and Singer had only previously engaged in brief talks about making another X-Men sequel.
During an appearance on U.S. morning show Live! With Kelly and Michael on Monday (03Dec12), he explained, "I mean they talked to me about it and I said, 'Wouldn't it be fun if it happened', and I didn't hear any more, and then suddenly Bryan Singer tweets his friends and says, 'I'm gonna make X-Men with Patrick Stewart and Ian McKellen', so that's how I learned that I got the job!"
Fassbender played a younger version of McKellen's good-guy-gone-bad Magneto in 2011's X-Men: First Class, while McAvoy portrayed Stewart's wheelchair-bound Professor X in his youth.