JANEANE GAROFALO just got divorced on Saturday after 20 years of marriage.  And here's the funny part:  She and her husband didn't know they were even husband and wife.  That's right:  They were married for 20 years and had NO IDEA.

Janeane dated Rob Cohen, who's a producer on "The Big Bang Theory", in the early '90s.  And one night in Vegas, they got hitched at a drive-thru chapel.  Janeane says, "We got married drunk in Vegas . . . We dated for a year, and we got married at a drive-through chapel in a cab."  The thing is, they didn't think the marriage was legit because they didn't, "go down to the courthouse and sign papers and stuff."  But it WAS. 

And the only reason they found out is because Rob is making plans to marry someone else.  Her name is Jill Leiderman, and she's a producer on "Jimmy Kimmel Live".  Apparently, Rob's lawyer stumbled upon the fact that he was already hitched.