He was old now, so old that he could feel Time stretching thin around him like the weight of his years was just too much. He had never been meant to be this old, to have this many regenerations, but one of the last acts of the Timelords had been to lift all bans on the numbers of regenerations to enable their warriors to fight on.
So that meant he had lost count of the numbers long ago, especially since what happened at Hartsfall, when regenerations had blurred together as he fought to save the world, bodies dying as fast as they were created.
Effectively, he was immortal. And by his side every moment was another with the heavy weight of the years on him, although he seemed to carry not a day of it. Captain Jack Harkness, now often called only "the Captain", was now his constant and only companion.
The Captain and the Doctor, roaming through space and time, righting wrongs, curing ills, were finally together as they found was only right. They had traversed the whole of space and time together, from the very blink of creation to the end of the universe, and millions of points inbetween.
The body he currently wore was one in the shape of a young woman. Through time he had taken on so many forms, from young boy to old man, from girl to crone, that no change surprised him now. He had been ginger, indeed, had been every race and colour possible.
The Captain, though, never changed, not a whisper, not a hair. The Doctor, far from feeling queasy when he looked at Jack now, felt still, at peace. Jack was a fixed point in Time, possibly the only one. Even the universe itself passes away.
They stood together in the TARDIS, looking out of the open door, holding hands, waiting in silence to see the end. On days like these they made a habit of it, when they felt themselves getting lost in the seething mass of time.
They stood, moving in time but not in space. And darkness fell as every star winked out, one by one. Everything died, grew cold. A deep stillness crept over all. And slowly, with infinite pain, the universe crunched back down until it was smaller than the head of a pin. All was black around them save the tiny point of light in the remote distance.
The Captain looked at the Doctor. The Doctor looked at the Captain. They liked this moment.
They stood still, hands clasped, long enough to take a breath, and everything exploded around them. This was not the old universe reborn, but something entirely new and different. This was an ocean of species unheard of by the last universe, a transcendence of thought unknown.
Another chance for Nature to prove herself.
Laughing with the pure joy of it, the Doctor kissed the Captain, and closed the TARDIS doors on the new universe.
"Here we go again," he said.