You might never have seen Marni Nixon on screen, but you’ll undoubtedly know her work even without realizing it.

A trained operatic soprano, Nixon made her Hollywood debut in 1947—not on the silver screen, but at the Hollywood Bowl in a performance of the composer Carl Orff’s opera Carmina Burana. That extraordinary classical experience brought her to the attention of the movie director Victor Fleming, who hired Nixon the following year to provide the singing voices of a heavenly choir of angels who serenade Ingrid Bergman in Joan of Arc. That role in turn led to Nixon being hired to dub the actress Margaret O’Brien’s singing voice in 1948’s Big City—and from then on, Nixon became Hollywood’s go-to “ghost singer,” hired to redub the singing voices of countless less vocally experienced movie stars.

Over the next two decades, Nixon’s impeccable singing voice was dubbed over the likes of Natalie Wood in West Side Story, Audrey Hepburn in My Fair Lady, and Deborah Kerr in both The King and I and An Affair to Remember. Nixon also provided the singing voice of one of the nuns in the convent in The Sound of Music and was even hired by Disney to provide the singing voices of the animated geese in Mary Poppins, and a bunch of singing flowers in Alice in Wonderland.

Then in 1953, Nixon was hired by the director Howard Hawks to provide the singing voice of the showgirl Lorelei Lee, played by Marilyn Monroe, in Gentlemen Prefer Blondes. Knowing that Monroe was not a particularly strong singer, Hawks and the studio executives originally wanted Nixon to rerecord all of her musical numbers. But in an interview in 2007, Nixon admitted that she had refused, telling the studio that doing so was an “awful” idea as Monroe’s breathy vocals matched her on-screen persona perfectly. Instead, Nixon agreed to redub only a handful of the most musically difficult passages and notes in the film, and so ended up rerecording merely in the high-pitched “no, no, no, no!” refrain that kicks off Diamonds Are A Girl’s Best Friend, and the single, vocally tricky line, “these rocks don’t lose their shape.”

The rest of the track—thanks to Nixon’s intervention—remains entirely Marilyn’s work.