The last show of Taylor Swift's 'Speak Now' tour was a special occasion indeed -- and so the country-pop cutie wanted to commemorate it accordingly. "On special occasions, you want to be surrounded by your friends," Swift told the crowd at Madison Square Garden. "One of my best friends -- she is such an amazing singer, and in four years of being best friends, we've never sang onstage together. And I think that's just such a shame! But it just so happens, Selena's here tonight!"

With that, Selena Gomez marched out to raucous cheers and immediately launched into her hit, 'Who Says.' Swift danced alongside her bestie and contributed to the chorus and sang the second verse. The adorable duo then let the crowd do the work. "It's your turn to sing," Gomez commanded. "Or do you not know it?"

The duet was the latest in a string of special 'Speak Now' tour guests, including Johnny Rzeznik of the Goo Goo Dolls, Flo Rida, B.o.B., T.I., Usher, Nelly and Nicki Minaj.

At the end of the song, an emotional T-Swizzle had her own demand for the audience. "In three seconds," she said, "I want you all to let Selena know how much you love her. Three, two, one!" Based on the ear-shattering shrieks, they adore her almost as much as her best friend (or the Biebs!). The girls closed the performance with a hug, and as if they couldn't be any sweeter, Swift actually skipped when escorting Gomez offstage.

It seems like Swift saved her favorite guest for last!

Watch Taylor Swift and Selena Gomez Perform 'Who Says' Live in New York City