Carly Simon joins Taylor Swift for 'You're So Vain' on Red tour stop

Saturday night (July 27) at Gillette Stadium in Foxboro, Mass., Taylor Swift brought a very special guest on stage at this particular tour stop.

"Before I bring out my special guest, I have this question that I've always, always had and I think a lot of you probably have this question too," says Swift. "Who is the song 'You're So Vain' by Carly Simon really about? Ladies and gentlemen, Carly Simon!"

It's a nice bit of symmetry, since a good chunk of Swift's songs are about her ex-boyfriends. Though Simon's lyrics are a bit more cryptic and no one really knows who her song is about (except NBC bigwig Dick Ebersol, who paid $50,000 at a charity auction in 2003 to learn the subject's identity).

Who do you think the song is about?
Photo/Video credit: YouTube