Ian McKellen broke down in tears on the set of "The Hobbit" after becoming so frustrated filming green screen scenes with only visual aids to act opposite.

The thespian, who reprises his role as wizard Gandalf in the new Peter Jackson movie, found it difficult to shoot scenes on his own with just photographs for reference - and he reveals he threw a tantrum.

He tells ContactMusic, "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."