The veteran actor took on the role of headmaster Albus Dumbledore in the third film of the wizard franchise, Harry Potter and the Prisoner of Azkaban, after Richard Harris passed away in 2002.
Felton, who was a young teenager at the time, admits he was starstruck when he filmed a scene with Gambon – and became tongue-tied as a result.
He recalls, “I was a youngster and Michael Gambon – who plays the fabulous Dumbledore – he’s quite a guy, he’s an amazing actor. I remember working with him for the very first time with his four foot beard and crazy hair.
“It was a very nervous time and I actually forgot every line I was supposed to say. I felt so bad at the time, it was one of the worst experiences of my life. I had been practising those lines for weeks. They should have been in my head!
“I took him out and said ‘Michael, I’m so sorry, I can’t apologise enough’, and he insisted the amount of money he was on per week I could mess him up as much as I liked. He was a very sweet guy and made me feel very comfortable very quickly.”