River Song. Ok so I didn't like Rivers story arc as much as most other people. I feel like I would have liked her better if they had waited and she was more during Capaldi's time. And then her line of "he's so young" would have fit better if she had met 11 in the library. I just wish 11 and Clara had more time together I guess. 11 & Clara. 12 & River. My thoughts.