"Marni Nixon: Hollywood's 'invisible voice' dies aged 86" BBC News

"The singer appeared, uncredited, on many of the biggest movie musicals of all time - dubbing the voices for Deborah Kerr in The King and I, and Audrey Hepburn in My Fair Lady.
She also sang the high notes for Marilyn Monroe in Diamonds Are A Girl's Best Friend; and "ghosted" Natalie Wood's vocals on West Side Story...."

http://www.bbc.com/news/entertainment-arts-36883629

-vk-