When she won the Best Actress Oscar for her title role in Mary Poppins in 1964, Julie Andrews could scarcely believe it. In a 2019 interview, she explained that her shock win—for what was her debut movie role—hit her “like a bulldozer,” and sent her “into therapy and analysis” for some time afterward. But Andrews wasn’t the only person shocked that the Oscar should have gone to such an inexperienced star. In fact, behind her win was one of Hollywood’s most memorable casting disagreements.

Mary Poppins may have been Andrews’ cinema debut, but by the early 1960s, she had already amassed almost two decades of stage experience; she was an established star both on Broadway and on London’s West End. Her stage career even included originating the famous role of Eliza Doolittle in Lerner and Loewe’s musical My Fair Lady in 1956. The show proved an immense success, quickly establishing itself as the longest-running show in Broadway’s history. So, when moves were soon being made to adapt it for cinema, it was widely accepted that its hugely successful stage cast would simply make the move to the big screen alongside it.

That was certainly true of Andrews’ Broadway co-stars Rex Harrison and Stanley Holloway, who were promptly hired for the Hollywood version as soon as production was announced. Andrews, however, was not—and in her place, established film star Audrey Hepburn was cast as Eliza, despite the fact that she had little singing experience (and ended up having to be dubbed by legendary “ghost singer” Marni Nixon).

Consequently, Hepburn’s casting proved hugely controversial, and many fans of the Broadway show saw it as an unacceptable slight to Andrews. As a result, when both Hepburn and Andrews ended up being nominated for the Best Actress award at the Oscars—Andrews for Mary Poppins and Hepburn for My Fair Lady—many saw Andrews’ shock victory over Hepburn as a fitting payback for losing out on the role.