As we we learn in “Walk The Line,” Grey, who signed on for a mysterious “multi-episode” arc , is playing the actual mom of “Betty Nelson,” whose real name is Britney Dickinson. Over the last few weeks of Grey’s, fans have learned a series of bombshells about single teen mom Betty, the troubled girl Owen Hunt (episode director Kevin McKidd) and Amelia Shepherd (Caterina Scorsone) have been feen fostering since last season. In last week’s “Winner Takes It All,” Betty revealed her real name, the fact she had given Owen and Amelia a fake number for her parents — so they had been calling her friend who was posing as the “Nelsons” for months — and her actual parents had no idea where she was or that she had been pregnant. That means Betty’s real-life parents knew nothing about Leo, Betty’s baby whom Owen has taken as his own son.