Taylor Swift famously described herself as being "obsessed with her friends." Living up to her reputation as the ultimate celebrity BFF, the singer has been inviting her besties to join her on stage during her 1989 sell-out world tour.

But this time it was a Friends reunion of a different kind, as she was joined on stage by one of the stars of the long-running sitcom Friends, Lisa Kudrow. The 52-year-old actress, who played struggling musician Phoebe Buffay in the sitcom for a decade joined Swift, 25, for a rendition of her character's famed comedy song Smelly Cat.

Although Friends finished its 10 series run in 2004, Kudrow took the opportunity to revisit the eccentric Phoebe, as the pair performed an acoustic version of the song before the packed crowd at the Staples Centre.

Swift asked Kudrow: "What song are you going to sing, Phoebe?" The cult comedy song clearly held meaning for the Shake It off singer who has in the past described herself as a devoted cat lady, and has two feline friends of her own named Dr. Meredith Grey and Detective Olivia Benson. The pair sang the hilarious song completely straight, much to the amusement of the fans of the TV show.

Appearing just days after her Friends co-star Matt Le Blanc had walked the runway with Swift, the performance was also a memorable moment for Kudrow, who later tweeted her thanks to the singer. "So @taylorswift13 is THE best person I've ever met. That was fun. Thanks Taylor," she wrote.

But Kudrow wasn't the only friend Swift had lined-up to help her close the 1989 World Tour. Best pal Selena Gomez, 23, made a stunning entrance as she joined Taylor on stage for a duet of the star's single Good For You, sending fans into a frenzy.

And with no shortage of celebrity friends eager to make a surprise entrance, Swift introduced her favourite singer, pop star Justin Timberlake. This has been so hard to keep a secret — you have no idea," Swift told the crowd, clearly excited. "He's been a great friend to me and will be remembered as one of the greatest musicians of our generation. Justin hasn't performed since he became a dad, so I'm just honoured that this is his first performance. Anyone who knows me knows that this is my favourite artist. I am obsessed with his music. It is the one thing that everyone in the world has in common."

The pair performed Timberlake's smash-hit song Mirrors in a show-stopping moment on a star-studded night.

Swift has been paying homage to her idols and friends throughout her 1989 world tour having been joined on stage by A list stars from the worlds of film, TV fashion and music including Julia Roberts, Joan Baez, Little Mix, Ellen DeGeneres, Mary J.Blige, Alanis Morissette Lorde, and Chris Rock.

And of course, while Taylor proving she will always be there for her friends, she also shared a special moment with her girl posse Cara Delevigne, Kendall Jenner and Karlie Kloss.