The star of the hit Fox TV show joined forces with the brunette beauty at the Trevor LIVE annual fundraising event at the Hollywood Palladium on Sunday night (05.12.10).
Both Darren - who performed 'Teenage Dream' on an episode of 'Glee' - and Katy have achieved chart success with the track, but until Sunday they hadn't performed alongside one another.
The actor initially took to the stage to sing the tune with Glee's Dalton Academy Warblers when the 25-year-old hitmaker joined him in a floor-length sequin gown for the final few lines of the track.
Darren told MTV News: "She's been really sweet. It's a great tune. I really lucked out that I got to sing that song. I mean, you've got to sing what they give you."
However, the pair weren't the only acts to wow crowds with their performance.