“Unfortunately she was a girl so it involved wearing a skirt. I know Ron isn’t a girl but I wanted to get noticed and show I was versatile.”

Rupert, who was 11 at the time, found out about the auditions from the BBC website for kids’ show Newsround.

He had to do half a dozen auditions after sending in his tape — which he didn’t enjoy.

Rupert admitted: “At the auditions you had to learn your lines and do a screen test. I had to do six or seven of them. I didn’t enjoy it because that’s a lot of nerves.”

Now 15, Rupert had only appeared in school plays before winning the key role as Harry’s best friend.

Overnight he went from ordinary schoolboy to film star. Slowly he is getting used to fame — and the attention of female fans.

Rupert said: “I get quite a lot fan mail from girls and a lot of them come up to me in the street.”

The ginger-haired star is not keen to take on romantic roles.

But in the movie Ron starts to fall for his friend Hermione so Rupert has had to deal with some “awkward” acting moments.

He reveals they have recorded scenes where the couple hug and hold hands — which shows new director Alfonso Cuaron has added spice to the film.

Rupert said: “There were some awkward scenes. There was a lot of hand-holding between me and Hermione. There were hugs as well but they got cut out.”

In the books Ron and Hermione do not hold hands until the fourth novel, The Goblet Of Fire.

Rupert said: “It’s weird doing romance. I’ve never been attracted to playing a romantic lead.”

He’s happier playing comedy. And Ron has plenty of witty lines — which Rupert delivers perfectly.

He said: “I don’t really take things seriously. Ron is a funny character and that is why I like playing him.

“I have always liked comedy films. I like Lee Evans. He’s cool. I would like to do a bit of comedy acting after Harry Potter.”

The fun does not stop when the cameras cease rolling, either. Rupert and Daniel Radcliffe, who plays Harry, have become great friends and enjoy causing mischief.

Rupert smiled and said: “Me and Dan made a crazy golf course out of stuff we found around thestudios. We made a windmill too, which we were going to power with an electric fan, but it was a bit dangerous.”

Rupert also draws cheeky cartoons of friends and fellow actors.

He said: “I do caricatures. I did Alan Rickman (Professor Snape) with a big nose. I wasn’t planning to show it to him but he crept up behind me and saw it.

“He asked to keep it, which was a relief. It was like being caught by my teacher. It was scary.”

Rupert, who will be 16 in August, does not enjoy school. He confesses he “forgets” to do his homework and will be happy to leave after his GCSEs next month.

He said: “I still get told off. I got a detention when I went back after filming because I didn’t do my homework.

“When the director set an exercise to help us get to know our characters, I was supposed to describe Ron but I forgot to do it.

“But Alfonso thought it was like Ron, so he was OK about it.”

Rupert has not yet finished JK Rowling’s fifth Harry Potter book, The Order Of The Phoenix which was released last summer.

He admitted: “I have read the beginning and it looks really cool.”

Perhaps it is Rupert’s busy social life which is holding him up.

He said: “I have started playing golf. I love go-karting too.” The young actor has treated himself with his wages from the three films.

He said: “I bought my own go-kart and golf clubs. I buy stuff I can enjoy. Some of my money is held in trust.”

But there is nothing Rupert enjoys more than being on set. He talks enthusiastically about stunts for the new movie.

Rupert said: “I get dragged along grass by a guy dressed in an all-in-one suit. In the film he is edited out and a computer-generated dog is put in his place.

“I really enjoyed the film. It’s really wicked.”

Rupert lives with his parents, Jo and Nigel, his four younger siblings and dog Ruby in Hertfordshire.

He said: “I still have to tidy my room. I have tried to stay really normal. I have a big family and that brings you down to earth.”

His youngest sister Charlotte used to believe he had magic powers.

Rupert said: “Charlotte was three when The Philosopher’s Stone came out and she thought it was real.

“When I fell off the horse she got really worried. Fortunately she hasn’t asked me to do any magic.”