During The Oprah Show's 24th season kickoff party, Harpo staff and more than 20,000 people pulled off a massive surprise for an unsuspecting Oprah. The entire crowd performed a choreographed piece to the Black Eyed Peas' "I Gotta Feeling," and Oprah was not only shocked, she was thrilled! Award-winning director Michael Gracey says the interaction between the Black Eyed Peas and the crowd is what made the flash mob so extraordinary.

"There's something really special when you take an audience and instead of just being passive and watching, you invite them to participate," he says. "That's why it was so magical for both parties. Two groups of people came together to create something that neither of them could have done alone."

Check out the flash mob that took over Chicago's Magnificent Mile!

Learn Oprah's flash mob dance!

24 kickoff party moments

More exclusive performances