David Thewlis was ''surprised'' when he was cast in the 'Avatar' franchise.

The 57-year-old actor will appear in the much-anticipated second and third films in the series, and he's admitted that it was ''entirely different'' to anything he previously experienced.

Asked about his time on set, David told Total Film magazine: ''I've got no idea what my scenes will be like because there are about 16 guys in the room with the video cameras but they're just shooting reference shots for Jim [Cameron] to look at later.

''What those guys are shooting will never be on the screen, what's being shot is obviously on these sensors. There are about 200 around the room, doing their thing.''

David teased details of his own character in the upcoming movies, which follows 2009's record-breaking original.

The actor also admitted to being shocked at having been offered a part in the franchise, describing his role as ''fantastic''.

David - who previously starred in the 'Harry Potter' franchise and the 2014 hit 'The Theory of Everything' - shared: ''I am a Na'vi, I'm a blue thing in it - which I didn't quite understand when I went to meet Cameron.

''I was quite surprised when I got offered that. I'm fascinated to see how I'm going to look, because they sort of make them look a bit like oneself. It's fantastic!''