Can you believe it's been 50 years since The Sound of Music hit theaters? Julie Andrews sure can't!

"Let's just say, I think it's a joke," the 79-year-old star quipped in a new interview. "I think someone pulled a fast one on me — I lost 20 years somewhere, surely it's only been 30 years!"

Though Julie admitted she doesn't go out of her way to rewatch the classic film "as a rule," she confessed she'll sometimes "bump into it, and it's like an old friend."

Julie during the filming of 'The Sound of Music' in 1965.

"The memories [from filming] are great, though — the pleasure of making it and the friendship with the children and Christopher [Plummer] continues, and I see him a lot, and the children are always in some contact one way or another," she lovingly said of her former costars.

Related Story: See Julie Andrews, Christopher Plummer and the Rest of 'The Sound of Music' Cast Then and Now!

As for why the movie — which won the Best Picture Oscar in 1965 — continues to enthrall generation after generation 50 years later, Julie said the answer is "obvious"!

Julie with her costars in 'The Sound of Music.' Photo Credit: Getty Images)

"Every 70 years, there's a new generation, but the film has to be good to last that long anyway!" she said on 'Good Morning America.' "It's got children and nuns… and beautiful scenery — somewhere in there is the secret."

Watch Julie's interview with Robin Roberts on 'Good Morning America' below.

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