In 1983, she said it is not about Mick Jagger, who contributed uncredited backing vocals to the song. In a 1993 book, Angie Bowie claimed to be the "wife of a close friend" mentioned in "You're So Vain", and that Jagger, for a time, had been "obsessed" with her. Simon made another comment about the subject's identity as a guest artist on Janet Jackson's 2001 single, "Son of a Gun (I Betcha Think This Song Is About You)", which sampled "You're So Vain". Simon said about the song, "The apricot scarf was worn by Nick (Delbanco). Nothing in the words referred to Mick."

Answer this question: who sang backing vocals on you're so vain? Let's think fast. Stream of consciousness:
The important part for answering this question is: In 1983, she said it is not about Mick Jagger, who contributed uncredited backing vocals to the song. So the final answer is Mick Jagger.