Taylor Swift welcomed a special "Friend" to the stage last night for a performance that is quickly going viral this morning. 

Former "Friends" star Lisa Kudrow made a surprise appearance at Swift's final L.A. show of her world tour. 

The duo gave the crowd a blast from the past as Swift and Phoebe Buffay performed the 1990s sitcom hit "Smelly Cat." 

In her intro of Kudrow, Swift joked that "she's only ever played in coffee houses ... never in a big venue like this."

Kudrow hilariously interrupted Swift during the duet, giving her some tips on how to really "feel the lyrics."

Swift also welcomed Justin Timberlake and Selena Gomez to her L.A. finale for special performances.

Watch the clip above. 

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