Which rockstar provided backing vocals for Carly Simon's "You're So Vain"?

For decades, people suspected that "You're So Vain" was actually about Mick Jagger himself, but he's just the guy singing with her in the background. Simon was recording with Harry Nilsson in London when Jagger wandered in and she invited him to sing along. Nilsson immediately stepped aside once he realized the vocal pairing of Simon and Jagger was the real magic. Jagger chose not to get credited on the song, probably because he was smart enough to know everyone would think it was about him.