Last weekend when Swift's "Red" tour reached Foxborough, Mass., she brought out Carly Simon, the woman who has kept listeners guessing for more than 40 years about the subject of her kiss-off song "You're So Vain."
"When I heard 'You're So Vain,' I thought, that is the best song ever," Swift said. "That is the most direct way anyone has ever addressed a breakup.... Every girl out there will be thinking of someone when we're singing."
The two sang it together Saturday in front of some 55,000 fans at
Here's the video with excerpts from the "You're So Vain" performance and interview footage of Swift and Simon, before and after their duet: