US pop singer Katy Perry gate-crashed at the Melbourne High School formal at the Grand Hyatt with her Australian girlfriend Ruby Rose. The two of them, being out on the town, decided on a surprise appearance at the school's event, sneaking into the ballroom of the hotel via a back door when her hit single California Gurls started playing.

All the teenage students went crazy after realizing Katy Perry was amidst them. Perry however left with Rose almost immediately after her song ended, but not before posing for lots of pictures.

Now Perry will be a tough person to book for next year's formal event of the school as well.

Rose tweeted recently saying she didn't know whose year 12 formal it was but there was no stopping Katy Perry. Even Perry made a related tweet on Twitter acknowledging her gate-crashing at the prom.

The duo carried on their big night on the town, partying at the Spice Market nightclub in the Grand Hyatt before hitting the Boutique nightclub in Prahran. Perry has departed from Melbourne yesterday and is currently at Tokyo.