Sir Ian McKellen is ''surprised'' by his new movie 'Mr. Holmes'.

The 76-year-old actor, who's previously starred in 'The Hobbit' and 'X-Men' franchises, plays the legendary detective Sherlock Holmes in the new crime drama film and has confessed he was taken aback that it's so ''sweet''.

Sir Ian explained: ''I was rather surprised. It's very very engaging and very sweet.

''It's about an old man, Sherlock Holmes, who is trying to solve his last mystery. It's the mystery that sent him into retirement and he is trying to solve what went wrong. Why didn't I solve it properly? Why did Doctor Watson write down lies all about this case?

''And he's helped out by a little boy and what is curious for me is that this all occurs just after the Second World War.''

Sir Ian also revealed he's set to sing in the live-action version of 'Beauty And The Beast', in which he plays the role of the clock.

He told BBC Radio 2: ''I play a clock. And my name is Cogsworth. And I get to sing. I'm sorry I'm not allowed to tell you what I sing. It's terribly exciting!''