Hours after celebrating the 40th anniversary of Saturday Night LiveTaylor Swift took to the stage at the afterparty, and was joined by legendary musician Paul McCartney and The Tonight Show host Jimmy Fallon.

TMZ obtained Instagram video of the post-broadcast festivities, which shows Swift on stage singing her megahit, "Shake It Off." McCartney is seen to Swift's right on the guitar and providing backup vocals, while Fallon is seen rocking out on the mic. Both McCartney and Fallon unleashed their inner Swiftie, as they both seemed to have enjoy performing to her joyful, carefree lyrics.

Swift, McCartney and Fallon are then seen singing The Beatles' 1963 hit, "I Saw Her Standing There." Swift even took the opportunity to show that she can strum a guitar side by side with a legendary musician.

Earlier during the Saturday Night Live 40th Anniversary Special, Fallon opened the show with a cold open with Justin Timberlake. McCartney then appeared briefly in the opening monologue and later performed the track, "Maybe I'm Amazed." Swift then showed off her acting chops in a revival of the sketch "The Californians" featuring Jason Sudeikis, Kristin Wiig and Fred Armisen, with special cameos by Bradley Cooper and Betty White.

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