You'd figure the one person who knew the most about Katy Perry is Katy Perry, but she had trouble beating a superfan in a Katy Perry trivia challenge on Jimmy Kimmel Live.

The talk show host invited the singer and a fan to play Who Knows Katy? “How well do you feel that you know Katy Perry?” Kimmel asked Perry, who responded, “Very well. I’m ready to play me.”

The fan, named Emily, walked out in a kimono and gave a few examples of her fandom. She said she had a wall covered with Katy until her boyfriend made her take it down. "At least you have a boyfriend," mused Katy.

The two were then tasked with buzzing in first to answer questions like, "What are the name of Katy's parents?" "Which 'American Idol' contestant with Perry write songs for?" And, "What was the first film to have Perry on its soundtrack?"

So who won? Well, you'll have to watch the video...