The actress read for the role in 2007 and was even said to have taken singing lessons in the hope of landing the part of Eliza Doolittle, made famous by Audrey Hepburn in the 1964 musical.
She said of the My Fair Lady remake last year (09), "I auditioned for it about two years ago, and I think it's been a matter of trying to assemble the correct team to do it that is going to make as interesting a movie and as good a movie as possible. There are good whispers going around, you know, and hopefully they'll come to fruition."
Knightley was never offered the part - and now she's taken herself out of consideration, according to Britain's Daily Mail.
An Education star Carey Mulligan is now tipped to take the coveted role.