Dr. Derek Shepherd (Patrick Dempsey) is going to propose marriage to Dr. Meredith Grey (Ellen Pompeo) on Grey's Anatomy. But there is one question besides the big question, and that's when will it happen? The mystery of Derek's plan is the focus of Thursday's big-deal Grey's Anatomy episode, which launches the Private Practice crossover and brings romance to, well, everyone. It's a very positive episode for the love affairs between Owen and Cristina, Lexie and Mark, Izzie and Alex, Mer and Der and heck, even for Callie, who is aggressively single at the moment. Want a taste of the good times? Check out the sneaks below!