He had missed her so much. She had always been so sassy with him, when they traveled together. Always taking charge, pushing him out of the way. She was his best friend back then. Never feeling anything stronger, just a good, solid friendship. And he regretted it so much, wiping her memory.
He wasn't allowed to see her, back then when he had his old face. That was the face that she knew, and he couldn't risk it with her. But now that he had regenerated, he could check in on her. Sometimes he'd hold open a shop door, or say hello on the street. Maybe smile in passing. It was great to see her so happy, with a good husband, a good job, and a good life.
But then her mother found him. He stepped out of his blue box and there she was, arms crossed with a disapproving frown. She was surprised to see his new face, so he explained his regeneration. She seemed to understand. And her face had softened a great deal when he told her that he was only there to see Donna again.
He went to leave the cafe where him and Sylvia chatted, and there was Donna, at the door, arms full of shopping bags. He opened the door for her. "Good morning," he said. "You look lovely today." And she did. Her eyes were bright and happy, and her red hair was shiny and shocking.
She smiled and said, "Thank you. I like your bow tie."
Her compliment made him happier than he had been in days. Grinning, he strode down the street. Donna liked his bow tie. She was the first one who had ever said that to him. He wasn't sure about his look, because Amy and River always made fun of it. But this sealed the deal. Donna liked it. And if she liked it, the others would just have to learn to like it too.
The Doctor straightened his bow tie, and tightened it on his neck. In honor of Donna Noble, he would keep wearing it. For her.