"It's not just a matter of memories, Jack, the timeline has been altered," he said, his voice calm and resigned. "You only remember because you're a fixed point in time, and whatever temporal distortion affected me washed over you. For me, it might as well have happened in another universe. I get vague feelings of it, but it's not the same."

It was cruel, he figured, telling Jack this. He could've just let him believe that it would be all right, that they'd remember eventually and be happy companions again. But somewhere in him, the Doctor believed that would be wrong. Like it would be breaking a promise he never made.

"I'm sorry."