Gaga rocked up to the gay night for a surprise appearance to sing her new song 'Venus', which was released today (click the video above to listen).
But she gave fans a little more than they (probably) bargained for when she lifted up her smock dress, pulled down her knickers and flashed her lady ga-garden to the crowd.
And after finishing the song, she did away with her dress altogether and exited the stage in the errrm, altogether.
As you do.
Fans at the show quickly took to Twitter and Facebook to share their bemusement at Gaga going all nudey in public, including 'Little Britain' star Matt Lucas, who tweeted: "Just saw Lady Gaga do a surprise set at G-A-Y. She got her arse out & showed her vagina. All agreed it was impressive but we're staying gay."
After the gig, Gaga tweeted: "Had an amazing night tonight at G-A-Y in London, after all these years you continue to inspire me. Can't wait for X-Factor tomorrow night!"