18 years ago, the popular TV show Seinfeld introduced a magical holiday known as Festivus, a wacky alternative to Christmas made up by George Costanza's father. What most people don't realize is that Festivus is actually based in reality. Seinfeld writers Dan O'Keefe and Jeff Schaffer told Uproxx the origin story of the holiday fans have come to love, and it's not what you think.

Here are a few things you didn't know about Festivus: 

1. Festivus was a real holiday that O'Keefe's Dad made up. 

“It is a fake holiday my dad made up in the ’60s to celebrate the anniversary of his first date with my mother, and it was something that we celebrated as a family in a very peculiar way through the ‘70s, and then I never spoke of it again,” O’Keefe said in the interview. 

Sources: Uproxx