In a night that will go down in concert history, Taylor Swift and Carly Simon shared the stage to sing the original breakup anthem "You're So Vain."

Gracing the stage at the Gillette Stadium in Foxborough during T. Swift's Red Tour stop in Massachusetts was one the state's music icons, Carly. The two sang the 1972 hit, which is much like Swift's series of odes to her ex-boyfriends (remember "Dear John", "WANEGBT" and "Forever and Always"?).

"When I heard 'You're So Vain' I just thought, 'That's the best song that's ever been written'," Swift told MTV backstage before the big duet. "That is the most direct way anyone has ever addressed a breakup. It's amazing."

The "22" singer may have taken songwriting points from Simon, who wrote "You're So Vain" about an ex-lover. However, unlike Swift's "Dear John", the 68-year-old singer's subject has not been revealed. According to the Los Angeles Times, though, Simon could have been singing about "Mick Jagger, Kris Kristofferson, James Taylor, Warren Beatty or the former Cat Stevens." Nevertheless, the duet was one for the books.

Onstage, Taylor wore her signature striped shirt and red short shorts, as she welcomed the icon to the stage.

"Before I bring out my special guest, I have this question that I've always, always had," Swift told the crowd, as noted by the LA Times. "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?"

The crowd went crazy as the 70s singer emerged onstage, wearing knee high boots, a glittery skirt, a hat and shades.

"Ladies and gentleman, give it up for one of your own, Carly Simon!" Swift told the concert crowd after the duet.

Swift tweeted her fangirl moment to her 31.5 million followers

"Got to sing 'You're So Vain' with Carly Simon at Gillette Stadium tonight!!!!! Unreal. I could not possibly look up to her more."

Taylor Swift will be continuing her Red Tour across America with her next stop in Iowa Aug.1. Who knows, Swiftie may have another historic duet in store for her fans.