The blonde actor – who has portrayed villainous Draco Malfoy in all of the films based on the novels by J.K. Rowling – admits he did not know who half of the cast of the movie were when he first signed up, even meeting legendary actor Gary twice before he understood he was playing Sirius Black.

He said: “I didn’t know who Gary Oldman or Michael Gambon were. I think I actually met Gary Oldman two times before realising that he’s an actor.

“I thought he was taking people on studio tours.”

However, Gary’s career was not the only thing Tom was surprised at when on the film – he also didn’t realise how big the series would become.

He added: “I was head over heels when I got the part of Draco, but I never imagined in a million years we’d be here 11 years later still talking about it.

“At that age, you don’t really grasp what you’re getting yourself in to!”