Watch Elton John and Lady Gaga Perform Together in Los Angeles

Duo sing "Don't Let the Sun Go Down on Me" at John's free, live streamed concert on Sunset Strip

Watch Elton John and Lady Gaga perform "Don't Let the Sun Go Down on Me" together at John's West Hollywood concert Saturday

On Saturday afternoon, Elton John hosted a free concert in Los Angeles at the old Tower Records building on the Sunset Strip, a live streamed performance that doubled as a thank you to the city of West Hollywood for hosting the rocker's annual fundraising Academy Awards viewing party. John's impromptu concert wasn't the only surprise the singer had planned as Lady Gaga, who will perform at the Oscars Sunday night, stepped onstage midway through "Don't Let the Sun Go Down on Me" to sing the track with John.

"The City of West Hollywood has welcomed the Elton John AIDS Foundation and our annual Academy Awards Viewing Party with open arms for many years, providing us with the perfect environment to host a really fun and special evening," John said in a statement prior to the concert. "We are profoundly grateful for their generous support, so I wanted to do something special just for them by giving our West Hollywood fans and supporters a surprise concert. Thank you, West Hollywood!"

Lady Gaga and Elton John previously performed together at the 2010 Grammys as well as during Gaga and the Muppets' Thanksgiving special in 2013.