'Sound Of Music' Producers Wanted Grace Kelly To Replace Julie Andrews

Secrets from behind-the-scenes of “The Sound of Music” are coming out ahead of the iconic film’s 50th anniversary.

Lady Gaga's beautiful tribute to The Sound of Music in honor of the beloved film's 50th anniversary was a highlight of the Oscars.

Fifty years later, the music can bring even a star-studded audience to its feet.

Now, a just-released book, The Sound of Music Story, is revealing surprising secrets about the making of the film which almost didn't become the enduring classic that we know today.

Author Tom Santopietro told INSIDE EDITION, "People were uncertain whether Julie Andrews would actually translate onto film because Mary Poppins hadn't been released yet. For the role of Maria, they considered Grace Kelly and Doris Day."

The original James Bond himself, Sean Connery, was among those considered for the role of Captain Von Trapp. Finally, Julie Andrews and a then little-known actor, Christopher Plummer, were given their iconic roles. But Plummer was conflicted.

"Christopher Plummer was a reluctant and cranky presence on the set. He was afraid he was going to ruin his reputation as a serious Shakespearean actor," said Santopietro.

Fortunately, his attitude matched that of his character.

Julie Andrews shot that iconic opening number in Salzburg, Austria, but it proved to be a major pain in the neck.

Santopietro said, "When the helicopter zoomed in on Julie Andrews, the downdraft from the helicopter was so strong that Julie Andrews kept getting knocked down into the mud."

The most dramatic part of the movie is when the Von Trapp family's escaped over the Alps. However, it didn't happen in real life.

"The Von Trapp's didn't escape over mountains into Switzerland. They took the train to Italy," said Santopietro.

But the Von Trapp's courage in the face of a Nazi occupation was the real deal.

Santopietro said, "In real life, they defied Hitler three times, and that is worthy of admiration."

Now, a whole new generation can get to know The Sound of Music through the voice of Lady Gaga.

"She had great love and respect for that music, and I think that really shined through. I think she wowed people," Santopietro said.