"I was doing a show at the National Youth Theatre, playing an old man. I went from 16st to 11st 5lb." "Toffee Crisp was my downfall. "My parents didn't overfeed me, nor did they make an issue of it. It doesn't have to be a problem for children to be fat, but it does affect you: you aren't as happy in that skin." His friends would joke about his weight, but it was never "spiteful".
Before that I had played fat clowns and I thought, 'If I want to have the career I would like, I am going to have to lose weight.' I was just starting drama school, and found I was moving around a lot. I once ate five at a sitting." He wasn't fat, he says, because he was unhappy, just self-indulgent. No doubt that has something to do with his sunny nature.
As a mother, I found it hard to laugh at Dudley Dursley because I used to worry about the actor playing him.
I feared that Melling was trapped in a Faustian pact: he could have all the fun and money that came from being in the Potter films but, in exchange, he had to be a bloated Bunter figure just to hang onto the part. "It was nearly two years ago," he says, refusing the offer of breakfast.
But there's no trace now of the piggy eyes and double chins in the 20-year old who is playing his first professional theatre role, as Mother Courage's son at the National Theatre.
The transformation of Harry Melling is as magical as anything that ever took place within J K Rowling's books, and it comes as a great relief.
Harry managed to get himself and Ron dates with Parvati and Padma Patil.Ginny Weasley was able to attend, as she was invited by a fourth year student, Neville Longbottom.All tournament champions were required to attend, and they must have a dance partner, as tradition required them to open the dance.It isn't his good looks that are so startling, it's his size.Like everyone else who has watched the Harry Potter films, I am used to Harry Melling in the guise of Dudley Dursley, Harry Potter's lard-bucket cousin.