Casper Smart's Dumb Move -- Reveals JLo's Deal with 'American Idol'

Jennifer Lopez must sure think Casper Smart is cute, because upstairs there's a vacancy -- he just ruined her big announcement that she's returning to "American Idol."

Smart was promoting his new show -- yes, anyone can -- when he was asked if his GF was coming back to the struggling show. He dug deep and said, "Yes."

Apparently Casper thought the cat was already out of the bag.