Super famous guest stars are always fun to see on TV shows.
But some guest stars are better or wilder than others. Like when Prince (!!!) guest-starred on New Girl.
Sometimes, the guest star isn't even an actor — it's some other public celeb or figure you can't even believe appeared on the show, like President Joe Biden on Parks and Recreation.
One of my favorite guest star stories is when Bruce Willis appeared on Friends because he lost a bet to Matthew Perry.
I also loved when Lady Gaga appeared on Gossip Girl. Gaga actually decided to do the guest spot because her little sister was a huge fan of the show, and she met with the producers first to make sure she could do the performance she wanted.
Now it's your turn! What's your favorite celeb guest-star story? Let us now in the comments below (along with why you love the story/example so much) and you could be featured in an upcoming BuzzFeed Community article!