It's back to the mega-mansion drawing board for Ben Affleck and Jennifer Lopez ... we've learned they'll no longer be moving into a $55 million estate in Bel-Air.
Sources close to the seller tell us ... the deal fell out of escrow. Unclear exactly what triggered the collapse, but a buyer is always able to pull out during an inspection period ... so Ben and Jen pretty clearly decided there was something they didn't like about the pad.
TMZ was the first to point out Ben may have popped the question when Jennifer was spotted out furniture shopping with her daughter Emme and wearing a giant rock. She tried to hide the diamond once she and Emme left the store ... but it was pretty easy to spot.