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Taylor Swift is performing with a '70s music legend.  At her Foxboro, Massachusetts show Saturday night, the country-pop superstar welcomed Carly Simon  to join her in singing the 1972 hit "You're So Vain." 

Following the show Swift tweeted her excitement over performing with Simon, calling the experience "unreal."  Taylor added that she "could not possibly look up to her more." 

Taylor is said to be on board for a proposed film about Simon, Carole King, and Joni Mitchell.  But Swift reportedly has the role of Mitchell in the movie, which is based on the book Girls Like Us

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