Joaquin Phoenix has apologised to TV host David Letterman for his awkward appearance on his show.

The actor was interviewed on the 'Late Show with David Letterman' in 2009 and appeared with a thick unkempt beard, looked confused, mumbled, chewed gum and responded to questions with one word answers, while spending much of the segment staring at his hands, perplexing the host.

It has since been revealed Joaquin was acting in character on the show - unbeknown to the host or viewers - as part of spoof documentary 'I'm Still Here', which follows the star 'quitting' acting and lunching a rap career.

Appearing on the 'Late Show.' again yesterday (22.09.10), Joaquin apologised, telling David: "I mean, I think that you've interviewed many, many people and I assumed that you would know the difference between a character and a real person. I hope I didn't offend you in any way."

David replied: "Oh, no. Oh, no, no, no. I'm telling you, it was so much fun. It was batting practice, you know what I mean? Every one of them was a dinger."

David also clarified he had no idea Joaquin was in character, asking him: "Was there a script that you and I were working with?"

To which Joaquin told him "no".

The segment on the show ended in much less awkward circumstances than their 2009 meeting, which David concluded by saying: "Joaquin, I'm sorry you couldn't be here tonight."

'I'm Still Here' was directed by Casey Affleck and is in cinemas now.