The soprano, real name Margaret Nixon MCEathron, passed away on Sunday (24Jul16) in New York following a battle with breast cancer, according to the New York Times.

The classically-trained singer's dubbing work was a poorly kept secret in Hollywood, although many studio executives tried to cover up her involvement at the time. Nixon's singing voice was most notably used to replace Deborah Kerr's in the 1956 movie musical The King and I and 1957 romance An Affair to Remember, Natalie Wood's in 1961 classic musical West Side Story and parts of Gypsy, and Audrey Hepburn's in My Fair Lady.

Nixon began her movie dubbing career in 1948 when she voiced angels in Joan of Arc before she moved on to provide the singing voice for Margaret O'Brien in Big City and The Secret Garden, and hit the high notes for Marilyn Monroe in Diamonds are a Girl's Best Friend in Gentlemen Prefer Blondes.

“You always had to sign a contract that nothing would be revealed,” Nixon told the U.S. news show Nightline in 2007. “Twentieth Century Fox, when I did The King and I, threatened me... They said, if anybody ever knows that you did any part of the dubbing for Deborah Kerr, we’ll see to it that you don’t work in town again.”

The singer wasn't always behind-the-scenes - she first appeared in front of the camera as Sister Sophia in 1965 musical The Sound of Music, and was credited for a number of singing voice roles including Jeanne Crain's in the original Cheaper by the Dozen and Janet Leigh's in Pepe, and she later recorded the singing parts for Grandmother Fa in 1998 Disney animation Mulan.

Nixon made a string of appearances on the stage, including musicals Nine, Follies and My Fair Lady, and was nominated for two Grammy Awards for classical recordings of songs composed by Arnold Schoenberg and Aaron Copland.

She also toured the U.S. with one-woman show Marni Nixon: The Voice of Hollywood, hosted kids show Boomerang in 1970s and 80s, and released a memoir I Could Have Sung All Night in 2006.