When Jamie got the part, he didn't know what a big deal it was. He hadn't read the books and had no idea how huge they were.
"I'd seen the book," he told The Leaky Cauldron. "It looked kind of boring with this kid on the front."
Fans
He quickly met Tom Felton, who plays Draco, and they sat and played PlayStation while the casting people brought in prospective kids to play Goyle.
Not long later, filming started on Harry Potter and the Philosopher's Stone.
Now with two movies under his belt, Jamie can hardly go anywhere in his hometown of London without being mobbed by Potter fans wanting his autograph.
And things will no doubt get even crazier when Azkaban is released in June.
Impressions of Ron
But success will not go to Jamie's head.
"It'll all go won't it?" he said simply. "The movies will end and the money will run out. When I go home, I'm just me."
On set, Jamie is good mates with the cast. Him and Tom Felton have stayed the best of mates, as has Joshua Herdman who plays Goyle.
He also keeps everyone laughing with his wicked impressions of Rupert Grint (Ron), Matthew Lewis (Neville) and directors Chris Columbus and Alfonso Cuaron.
Bum double
Jamie likes playing the joker - he even says he'd like to play Ron if he could be any other Potter character.
And he's happy to do stupid things on set - even pose for a bum double!
There's a scene in PoA where Crabbe gets kicked in the bum and then has to chase Malfoy while his trousers are falling down.
But the crew wouldn't let Jamie get kicked in the bottom, so he had to bend over in front of the whole set and have his bottom compared to extras to find a perfect match.
Potter baddies: full interview
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