Simon Cowell has TWENTY THOUSAND reasons to cry over Thursday night's "X Factor" results show -- and it's all thanks to a rich-person bet he made with L.A. Reid.
TMZ has learned ... Simon and L.A. made a wager at the beginning of the season ... and if either judge had a contestant win the whole shebang ... the losing judge would cough up $20k.
So when L.A.'s contestant Tate Stevens took home the crown ... he grew just a tiny bit richer than he already is. And since Simon's no sore loser, we're told he plans on cutting the check ASAP.
We're pretty sure it's illegal for the rich people to make this bet in the State of California -- but hey, who are we gonna tell?