Back in 2006, Reid 86'd Gaga from Epic Records ... and now calls it "the biggest mistake of my career."
He recently explained the whole situation to FOX 5 saying, "I feel a little bad about it. I do. I feel bad. I signed her. She comes in, she plays the piano, she’s incredible, she sings, I sign her, I tell her she’s going to change music. A couple of months later I say, maybe I wasn’t right. Maybe I don’t like this so much and I make the biggest mistake of my career. I dropped Lady Gaga."
Good news ... they managed to move past it -- and he's still a huge fan.