On Tuesday, Taylor Swift wrapped up the U.S. leg of her Speak Now Tour with a second showing at New York City's Madison Square Garden, and as expected, she went out with a bang. The 21-year-old country-pop hitmaker invited two guests to the stage to help her close out the tour: her best friend Selena Gomez and the legendary James Taylor.

Swift teased the millions of fans outside of the Big Apple who couldn't attend by tweeting photos of her guests' dressing room signs, but that was nothing compared to the excitement inside of the Garden. The 'Ours' songstress told the audience that being that it was her final show in the States, their concert was an extra special occasion.

"On special occasions you want to be surrounded by your friends," she continued, teasing Gomez's introduction. "And one of my best friends, she is such an amazing singer. We, in the four years of being best friends, have never sung on stage together, and I think that is just such a shame. So it just so happens … It just so happens Selena's here tonight."

As the room shook with screams, Gomez -- whose boyfriend Justin Bieber performed with Swift during her four-day run in Los Angeles -- took the stage to perform her hit song 'Who Says.' Together, she and the main act danced around in sparkly dresses as the sold out crowd sang in unison.

But Swift saved perhaps the best act, or at least the best story, for last. As she sat on her couch at the center of the stage, she began to recall her school girl days of being in chorus class. She informed the audience that she once told her mother she didn't like any of the songs they would sing -- except one. "Just because we get to sing this song, it's my favorite class," she added, calling 'Fire and Rain' "probably one of the most fantastic, amazing songs I've ever heard in my life."

That was the same moment when her mom told her, for the first time, that she is actually named after James Taylor. Swift teased the crowd, "The funny thing about playing Madison Square Garden is that magical, magical things can happen. You never know if James Taylor might just walk out onstage," enticing the five-time Grammy winner to take the stage beside her and perform her favorite song.

The 'Fire and Rain' duet led into Swift's 2009 single 'Fifteen,' accompanied by Mr. Taylor on guitar. Following the show, she tweeted, "I have so much to be thankful for this year. I'm leaving New York, replaying this tour in my mind. I love you all so much."

The Speak Now World Tour picks up overseas in March in Australia.

Watch Taylor Swift Perform 'Fire and Rain' With James Taylor

Watch Taylor Swift Perform 'Who Says' With Selena Gomez