'Saving Mr. Banks' Tells Surprising Backstory to 'Mary Poppins'

INSIDE EDITION caught up with stars of the new movie Saving Mr. Banks and the original Mary Poppins about the back story of the timeless movie.

It was a star-studded hollywood premiere where voices from Hollywood history rang through.

The making of the classic movie Mary Poppins is the subject of Saving Mr. Banks starring Tom Hanks as Walt Disney and Emma Thompson as the notoriously prickly Poppins author P.L. Travers.

Tom Hanks told INSIDE EDITION, "I think Walt thought he would charm the socks off her. He was Walt Disney for crying out loud. Everybody loved him, and when it didn't work like that, I think he was flumoxed."

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The author at first refused to let Disney make Mary Poppins. She feared the message at the heart of her magical nanny, who's blown into the home of the Banks family, would be lost in all the Hollywood glitz.

Little Jane Banks was played by Karen Dotrice. She's now 58 and a mom of three.

INSIDE EDITION's Jim Moret asked Dotrice, "When you saw the film Saving Mr. Banks, were you surprised by the back story?"

"Yes, that was shocking. It was really interesting because I knew nothing about this until I saw Saving Mr. Banks. They kept all of that hidden from the kids."

P.L. Travers was particularly attached to her story because it was inspired by her own unhappy childhood. Her father was an alcoholic who died when she was just seven years old.

Emma Thompson told INSIDE EDITION, "All the time you're watching her child part and how that child part was wounded."

At the end of Mary Poppins, the hard-hearted Mr. Banks learns that the love of his children is all that matters.

"She was there to save the family, and to save the head of the family," said Dotrice.

When Disney agreed to tell that side of the story, Travers finally signed off. The rest is movie history.

And here's something you may not know. "Feed The Birds," the haunting lullaby Mary Poppins sang to the children, was Walt Disney's favorite song ever.

Rare footage of the 1964 premiere of Mary Poppins shows the 28-year-old Julie Andrews' at her very first movie. Fifty years later, the legendary star still sparkles in the spotlight.