renee zellweger bradley cooper splitnaughty but nice rob shuterBradley Cooper and Renee Zellweger have broken up, leaving family, friends and fans to ask ... what went wrong?

"They were such a great couple that we are all shocked," a friend of Renee's tells me. "We all thought for sure they were going to be together forever after they moved in together last fall -- we're really sad."

My source says Renee even skipped the Golden Globes in January to be with Bradley when his father died. "But after that she wanted a ring, and he just wasn't ready to propose," the friend tells me.