Sir Ian McKellen has revealed that he burst into tears of frustration on the set of his upcoming film The Hobbit.

The 73-year-old actor plays the wizard Gandalf in the Peter Jackson directed film, a prequel to the Lord of the Rings trilogy.

He told ContactMusic that he became upset while filming a sequence on green screen with only visual aids to act against.

He said: "In order to shoot the dwarves and a large Gandalf, we couldn't be in the same set. All I had for company was 13 photographs of the dwarves on top of stands with little lights - whoever's talking flashes up."

"Pretending you're with 13 other people when you're on your own, it stretches your technical ability to the absolute limits."

"I cried, actually. I cried. Then I said out loud, 'This is not why I became an actor'. Unfortunately the microphone was on and the whole studio heard."

The first movie in the three-part Hobbit series,Hobbit: An Unexpected Journey, The (2012), is due for release on December 13 in the UK and US.

Source: Press Release