(CNN) Dick Van Dyke paid a pretty penny to play two roles in "Mary Poppins."
As part of Thursday's "20/20" special, "Mary Poppins Returns: Behind the Magic," Van Dyke told Lin-Manuel Miranda that he asked Walt Disney for permission to play Mr. Dawes Sr., the banker, as well as Poppins' good pal, Bert, in the 1964 classic.
But Disney said no -- unless Van Dyke paid for it.
"I had to go to Walt and ask him for the part. He wouldn't give it to me," Van Dyke said. "I said, 'I'll do it for nothing.' Actually, I had to give him $4,000. I paid him to do the part."
Van Dyke doesn't regret it one bit. "And I'd do it again!" he said.
Related: 'Mary Poppins Returns' dazzles with new trailer
A sequel to the original, "Mary Poppins Returns," starring Emily Blunt as the magical nanny made famous by Julie Andrews and Miranda as Bert, is set to premiere December 19.