Author's Notes:
NB: This would require the ending of ‘Twice Upon A Time’ to fade out at the point of Capaldi’s regeneration, right before Whittaker’s eyes appear.

At the conclusion of ‘The Time of the Doctor,’ the 11th Doctor mistakenly thought that the Time Lords were granting him a completely new regeneration cycle. They weren’t. They granted him *one more* life to enable him to complete his work on Trenzalore and defeat the Daleks.

During ‘Twice Upon A Time,’ the 12th Doctor is struggling with the decision of whether to regenerate or to refuse, unaware that this was his final incarnation. Ultimately, this decision is taken out of his hands. As he regenerates, the artron energy dissipates into the heart of the TARDIS. The Doctor has passed away. The TARDIS travels on and reconstitutes the Doctor’s personality and memories to create the being known in ‘The Day of the Doctor’ as ‘The Curator,’ an artificially generated being that is able to shape itself into different forms of the Doctor’s past faces (ie an older fourth doctor, maybe a younger first doctor, younger seventh doctor, older ninth doctor etc). It remains as a monument to the Doctor’s history and ensures that his work lives on.

“Laugh hard. Run fast. Be kind.”

Regeneration was always a risk; the Doctor knew this. There was always a chance that he’d be blown to atoms or malformed in some way. This was the end for this incarnation. He was tired. He’d been struggling whether to continue or simply to finally rest. He’d told his friends at the time that the Time Lords had granted him a whole new regeneration cycle. But, really, deep in the pit of his stomach he knew there was always a possibility that it wouldn’t last, that it’d be a one-off. It wasn’t like the Time Lords to be gracious, after all. Now, with his life ebbing away, he had one last thought: what have I got to lose by trying again?

“Doctor… I let you go.”

The Doctor flung his arms back as he was gripped by the intense explosion of artron energy as his skin started to boil. He could feel everything slipping away from him as he closed his eyes. The TARDIS control room was filled by a bright light as sparks and flashes of flame engulfed the cavernous space. And then…

The light faded. There was no sign of the Doctor. The TARDIS hummed and whirred and fell silent, as it contemplated a universe without its hero.

As the TARDIS quietly spun through the vortex, it was like a funeral cortege. All was quiet.

Click. Click. Whirrrrrrr. The column slowly began to rise and fall, as though inhaling and exhaling. A cloud of artron energy began to form a ring around the console. There was suddenly a warm feeling around the control room as the flame coalesced. A human shape began to form. Out of the flames emerged a hand. The hand simply clicked a switch on the console and a blinding light consumed the figure.

The figure standing in front of the console was confused, at first. He grabbed the scanner screen and was surprised to see a familiar yet unfamiliar face staring back. He was dressed in a simple black suit with white shirt and black shoes, not unlike what the Doctor was just wearing. He clutched his head as a searing pain dug into his temples. He collapsed to the floor.

Upon waking, he felt a great sense of clarity. He rose slowly to the console, a grin on his weathered face. He was compelled to press a combination of buttons on the console. And then the TARDIS’ hologram protocol activated.

Stood in front of the man was a hologram of the Doctor’s previous incarnation, all eyebrows and wild stare. He was solid yet also artificial as he began to speak.
“This is TARDIS protocol zero zero fourteen zero. If you are seeing this, then the Doctor is no more. I hope he didn’t make too much of a mess, old girl. You are a part of the TARDIS now, a computer-generated lifeform designed to continue the Doctor’s work. Your appearance is randomly generated by the TARDIS to recall all previous appearances.” How incredibly vain, the lifeform thought. How very like the Doctor. “All information you need is contained in the TARDIS computer.” The hologram faded out.

The lifeform walked around the control room for what felt like hours, trying to adjust to his existence. He looked in the scanner screen again to study his face. “Incarnation number… four?” he asked. But he looked so much older than he remembered. The curly black hair had been replaced by a thick, white mane. His features were the same, just older. But the smile was unmistakable. It seems the Doctor hadn’t quite programmed the protocol correctly. He laughed. He laughed deeply and outrageously as he realised the truth of his existence- a monument to the Doctor’s work. And his vanity. It amused him that the Doctor had created a living exhibition of himself, especially after just meeting the Testimony.

A thought came to him. What was he going to call himself? He wasn’t the Doctor but he was to represent his work, like overseeing a museum. How about ‘The Conductor’? No. Silly. He wasn’t on a bus! He was curating a museum of sorts. Yes. The Curator. That’ll do it.

The Curator programmed the co-ordinates for parts unknown. He smiled. “Over to you, old girl.” And with that, he pulled down the lever on the TARDIS console as the column rose and fell. The TARDIS spun through the vortex, to new places.

To new adventures.