Video: YouTube star Keenan Cahill talks about, meets Katy Perry

YouTube sensation Keenan Cahill fulfilled his "Teenage Dream" when he appeared onstage with Katy Perry Friday at the Wells Fargo Center.

Cahill, 16, of Chicago, has a rare genetic disorder called MPS6, and credits Perry with his online fame after she tweeted about his lip-synched version of her hit "Teenage Dream." Cahill's lip-synched videos of artists such as 50 Cent and LMFAO have been viewed millions of times. We spoke with Cahill Friday before he met up with Perry. He said he once hoped to be an actor or singer and took to lip-synching on YouTube to promote himself, and it took off.

"I'm reaching my dream," he said. "I have a single coming out. Hopefully 50 Cent will be on it."

Tomorrow, Cahill goes in for surgery on his legs, another in a string of more than a dozen surgeries he has had related to MPS6.