When accepting the role, Hepburn was lead to believe that her singing voice would make it to the final cut. After all, she had sung in Funny Face and Breakfast at Tiffany’s (for an Oscar-winning song too). However, in the end, her voice was dubbed by Marni Nixon who, after letting the cat out of the bag, was shunned by Hollywood for a period of time. Nixon also dubbed Deborah Kerr in The King and I and Natalie Wood in West Side Story.

Julie Andrews originated the role of Eliza Doolittle on Broadway, but she had yet to have her big break on the screen. Given the $17 million budget, the studio was interested in a star – hence, Audrey Hepburn. Andrews, of course, did go onto great fame with Mary Poppins – which she wouldn’t have been able to do if she had starred in the musical adaption.

It took an hour for Hepburn to be dirtied up for her role as Doolittle, which included putting dirt behind her ears, under her nails, and on her face. It was especially hard for Hepburn to wear the heavy wool skirts and boots during the shoot because temperatures at the studio could get to over 100 degrees Fahrenheit during the summer.

It’s hard to believe that the studio thought of replacing the Tony-winning Broadway original Rex Harrison, but Cary Grant was offered the part. However, he turned it down believing he couldn’t play a dialectician. He jokingly said, “I sound the way Liza does at the beginning of the film.” Rex Harrison won an Oscar for his film performance.

“I have never sung any one of the songs the same," he reportedly said, refusing to sing to a pre-recorded track. As a result, the crew used a wireless microphone for the actor, so he could perform the songs live. For those paying attention, his microphone can be seen on his tie. Interestingly, his live performances caused a problem when restoring the film later on. His sound was too brittle, and it required his sound to be "warmed" to match the quality of others.

Warner didn’t want viewers to be able to tell that the movie was filmed on a studio set. So the production team worked hard to make each location seem as authentic and detailed as possible. They used real London homes and locations as a reference.

Restoration was required because the film negative wore down to such a degree that the picture began to fade, the colors turned pale, and the lack of definition hid the actors’ performances. The film was so brittle it required hours of patient work and problem solving to salvage it. Digital artists were instrumental in changing the quality of the final product, including removing scratches and dirt. The process cost more than $600 thousand.