The Doctor has loved certain people throughout history even without having to meet them. Sometimes the adage 'you should never meet your heroes' holds unfortunately true when he does inevitably come across them in person. Sometimes, however, they turn out to be everything he hoped.
He watches from a distance as Daenerys Targaryen stands up and proudly declares herself Khaleesi, and he knows he was right about her. There's something about a woman who decides to stand up and take control of her own destiny that's always captivated him.
He supposes it doesn't hurt that she's beautiful and blonde, either.