Katy Perry says she loved Glee’s cover of her hit song “Teenage Dream,” and on Sunday night she proved it.

The pop sensation surprised a Los Angeles audience at Trevor Live at the Hollywood Palladium when she joined the show’s Darren Criss for a first-ever duet of the popular tune.

Darren, a 23-year-old who plays Blaine, recently broke a Glee record by singing the show’s first number one hit on iTunes.

Katy not only joined Darren in the middle of the hit as a surprise performer, but she sang the Glee arrangement for her song.

No one expected Katy to show up, because she was booked across town at Jingle Ball at the Nokia Theater in downtown Los Angeles on the same night.

But the singer had so much fun at Trevor Live that she came back for the after party, telling RumorFix she returned “because I live just down the street.

The Trevor Project is the only 24/7 suicide hotline for gay and questioning teens.