The Canadian star appeared opposite Julie Andrews in the Oscar-winning 1965 musical, set in Nazi-occupied Austria, but admits he couldn't understand why fans would get so emotional about the film until he was forced to sit through a screening one holiday.
He tells People magazine, "People were unnaturally sentimental about the film. So I always gave it a tough time.
"But a few years ago, I went to an Easter party and had to watch the damn thing with these kids! I was a prisoner! And then I thought, it's got everything - the lovely songs, the Nazis and the nuns and kids. It's timeless, and I'm grateful to it."