The "Firework" singer turned 31 on Sunday and she celebrated over the following days with a museum trip and a dinner party at an Italian restaurant, reported Contactmusic.
She continued to toast the occasion on Tuesday by attending Madonna's Rebel Heart Tour show at The Forum in Inglewood, California, and she was roped in to taking part in the "Vogue" singer's saucy onstage segment.
After the performance, Madonna told Katy onstage, "Thanks... I know you didn't want to come up here and do this. So generous. A big round of applause for..."
The birthday girl reposted footage of herself busting impromptu dance moves as Madonna circles around her.