Watch Katy Perry's Teenage Dream-er

15 year old Keenan Cahill from Chicago has become one of YouTube's biggest hits of the year so far, posting parodies of some of his favourite hits.

Katy Perry is the latest star to have the Cahill treatment as Keenan posted a parody of her latest hit 'Teenage Dream' on YouTube. The Californian Gurl posted it on her Twitter page last night, along with the simple message 'I heart you @KeenanCahill'.

Check out the video and tell us what you think below: