Daniel Radcliffe has admitted that he struggled to keep a straight face on the set of the latest Harry Potter movie.
And the teenage star has laid the blame at the feet of veteran star Michael Gambon, who plays Harry's mentor Albus Dumbledore.
In an interview with Contactmusic Radcliffe said: "All the scenes with Dumbledore were quite difficult, but they were great fun. [Gambon] is wonderful and I love him and he's one of the greatest actors I've ever worked with.
"But it is amazing because he will be actively trying to make you laugh right up until the point the director says, 'Action'."
"I think I'll be vaguely happy with the scenes between myself and Michael. I think they'll be good. Because we got to like each other very much off screen, I'm hoping on screen that'll come across."
Harry Potter and the Half Blood Prince is the penultimate story in the series however the final film Deathly Hallows will be split into two movie.
The first of those movies is set for a 2010 release with the concluding part to hit cinemas twelve months later.
Tagged in Daniel Radcliffe Sir Michael Gambon