Sir Ian McKellen is ''quite a shy person'', according to the maker of a new documentary film.

Joe Stephenson has directed 'McKellen: Playing The Part', which is built around a 14-hour interview that explores McKellen's dramatic life story, and the filmmaker has revealed there's a marked distinction between the actor's outgoing on-stage persona and his more reserved real-life self.

Speaking exclusively to BANG Showbiz, Joe explained: ''He's a very gentle and quite a shy person, really. Which is quite a strange thing - a juxtaposition, really, with how outspoken he is about things and how brave he is and how much of a strong performer he is. He is actually quite a shy individual.

''The thing that surprises me about him is that he's not as certain about himself as I thought he was. I had an idea of just age being a thing, like when you get to a certain age you must be certain about yourself, and you must really know everything. He doesn't - then I just think maybe nobody really does.''

Joe claimed McKellen approaches many of his public appearances like a stage performance, meaning he doesn't allow other people to get too close to him.

But because he's earned the actor's trust, McKellen was happy to speak honestly about his life during the film.

Joe said: ''I think if it was somebody he didn't know asking the questions that barrier would be up, and I don't think it would be really possible to penetrate.

''Naturally, I think the first day or so it felt very much like that barrier was up a little bit.

''But the more he eased into it, the more he realised I wasn't after any controversy, I wasn't after something that was going to be headline-y. He got to relax and understood that's not my intention.''

'McKellen: Playing the Part' will be broadcast live to cinemas across the UK on May 27.

To find your local cinema, visit mckellenfilm.com.