The bond between the members of Girls' Generation is still going strong!

During the March 16 stop on Tiffany Young's 'Lips On Lips' tour, which was held at the Troubadour in Los Angeles, the singer invited a special guest on stage - none other than fellow Girls' Generation member Sooyoung. While on stage, Sooyoung greeted the fans and joined Tiffany for a brief a capella performance of "Into The New World," their classic debut single.

Fans following Sooyoung on Instagram could also see that, prior to being on stage, she had been supporting Tiffany as a member of the audience, taking clips of the performance and playing around in Tiffany's dressing room backstage.

Meanwhile, the March 16 concert was the very last of Tiffany Young's 'Lips On Lips' tour. Earlier that day, the singer took to her personal Twitter account to reflect on the tour with fans, writing: "Oh my god, tonight is the last show. [...] The 'Lips On Lips' showcase tour will be forever in my heart."

Check out Sooyoung and Tiffany's "Into The New World" performance above!