We mourn the loss of singer Marni Nixon, whose provided the voice for musical numbers in films from “Gentlemen Prefer Blondes” to “West Side Story.”

She sang for Deborah Kerr in “The King and I.”

She sang for Audrey Hepburn in “My Fair Lady.”

She sang the operatic flourishes at the beginning of Marilyn Monroe’s “Diamonds are a Girl’s Best Friend.”

And she sang for Natalie Wood in “West Side Story.”

She appeared on screen and did her own singing as a nun in “The Sound of Music.” Here she sings some of the songs from the film as a guide for the singers who would be dubbing the international editions.

The New York Times reported that Hollywood tried to keep her participation in the films quiet.

Ms. Kerr was nominated for an Academy Award in 1956 for her role as Anna in “The King and I”; the film’s soundtrack album sold hundreds of thousands of copies. For singing Anna’s part on that album, Ms. Nixon recalled, she received a total of $420.

“You always had to sign a contract that nothing would be revealed,” Ms. Nixon told the ABC News program “Nightline” in 2007. “Twentieth Century Fox, when I did ‘The King and I,’ threatened me.” She continued, “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.”

Ms. Nixon had an extensive career in theater and concert performances but is best remembered for the films the producers did not want anyone to know she sang in. May her memory be a blessing.