In a fun twist, that very artist — Carly Simon, of course — joined Swift on stage Saturday in Massachusetts for a duet of her famous/infamous mystery slam, "You're So Vain."
Swift is an expert at writing songs rife with clues about which hapless ex she's skewering, but even she admits Simon's classic tune has stumped her — as well as countless other music fans, who've debated for decades the identity of the self-absorbed lover in the 1972 hit.
"Before I bring out my special guest, I have this question that I've always, always had," the superstar told the crowd at Gillette Stadium. "I think a lot of you have probably had this question too, always wondered what the answer is. Who is this song, 'You're So Vain' by Carly Simon, written about?"
Simon then came on stage, and although she did not answer Swift's question (no surprise there; she's never confirmed who the song is about), the pair treated the audience to what is probably one of the most fun/ironic duets in recent memory: One artist famous for oversharing in regards to her lovelife, the other known for keeping her mouth tight shut!
Like Swift, Simon has teased her fans with little clues about the song's subject, including revealing letters in his name (a tactic Swift mirrored by capitalizing letters in her lyric sheets). Popular guesses over the years include Mick Jagger, Kris Kristofferson, Warren Beatty, David Geffen, and Cat Stevens. The mystery is so abidingly popular that Simon has an entire section devoted to it on her official website.