"Will you still love me when I'm old?"

The Doctor looked up. Clara was looking at him with sudden intensity. The question had come out of nowhere. "I-" he stuttered. It was hard for him to find the words. It was a subject he forced himself not to think about terribly often. The idea that she would age and expire whilst he remained the same was a terrifying one. But now her wide brown eyes were on his, expectant, nervous, uncertain, and he couldn't do anything but reassure her. "Yes," he promised. "Of course I will. Forever."

And he would. Because the Doctor didn't go back on his promises, and because love for him was a rather big deal. He was so much older than her already. Age wouldn't tear them apart. For better or for worse, he'd love her for as long as they both lived.

Clara was twenty-four when he promised her that. When she was twenty-five she began working as a teacher. Her excitement about this was indefatigable, and he felt pride welling up inside him as he watched her diligently battle through her work, determined to impress early on in her profession. He kissed her goodbye on the morning of her first day in her new job, catching that faint aroma of English breakfast tea and spearmint gum that he'd come to associate with kissing Clara, and gave her a fond smile. "You ready?"

Clara looked nervous. "No," she admitted. "What if I'm rubbish at it?"

"You won't be." He smiled at her encouragingly. "Go on. Break a leg."

Clara grinned back at him. She turned away and disappeared out the door. "I love you," she called out as she departed.

"I love you too." And he did. One year on, and he loved her just as much as he ever had.

When Clara was twenty-nine, she began writing her first novel. After four years of working in a secondary school, and armed with a wealth of stories from across the stars, she felt she could create the next young adult fantasy hit. The Doctor contributed his own extensive experience to it, let her sound ideas off him and gladly read through it when she was finished. By the time she was thirty she'd successfully published the first book in her series, The Great Intelligence, to a generally positive response from critics and a well and truly brilliant one from the kids themselves. Suddenly his partner was a woman very much in demand at conventions and bookshop openings and whatnot, and he couldn't help but feel pleased for her watching how much delight it brought her. His Clara Oswald had made a name for herself.

"You're a celebrity now," he informed her.

Clara sighed in good-natured exasperation. "The kids won't shut up about it. They're all trying to figure out if any of the characters are based on them."

"And are they?"

She smiled slyly. "Maybe a few. But hey, don't give me all the credit. You were great for ideas. Everyone loves that villain, the shadows that eat people alive. Honestly, I don't know where I'd be without you." Clara paused thoughtfully. "Actually, I know exactly where I'd be. In someone else's house, taking care of their kids, still trying to sort my PGCE out and thinking this was all life was. Except you came along."

They exchanged a sweet look. The Doctor could lose himself in Clara's eyes. They were like two tiny brown planets, shimmering with continents of thought and oceans of wonder. It made him happy to think of the things they'd seen because of him, and that someone had been there to share them with him. "I love you, Clara," he said simply. And indeed he did. Six years from when he'd said it before, and it was as true as ever.

Clara kept on writing. She stayed in work as a teacher, even though she could comfortably have retired on the royalties. "'Don't quit your day job,'" she said. "That's what people always say." She didn't quit her day job, though she kept on growing more famous. Midway through writing the fourth book, she was approached by a film company interested in making the first into a movie. A lot of shrewd negotiating went on, and by the end of it Clara had somehow managed to get the whole thing done on her terms and still ended up rather richer than before. They spent Clara's thirty-fourth birthday at the premiere of the movie, which earned as good a reception as the book had. Clara, too, was wonderfully received, and not just for her writing skills.

"Everyone's looking at you," the Doctor remarked. "You look incredible."

She did. Clara, to his eye, was the most beautiful woman in the universe. Tonight, quite superbly made up by the same team that did the make-up for her film's stars, his little Lancashire rose was resplendent in a dark blue gown of which a number of nosy fashion magazine photographers were rushing to take pictures of at every opportunity. Clara ignored them all to smile at him only. "Not so bad yourself."

The premiere segued wonderfully into a delightful after-party. He and Clara drank and danced and laughed, rather a lot more than they probably should have done. They staggered back giddily to the TARDIS in the early hours of the morning, went home and fell into bed together. Soon that gown the photographers had been so obsessed with was on the floor, and the rest of the night passed in a haze of passion. Finally, exhausted and tipsy and sleepy and wholly content, they collapsed into each other's arms, aware in the darkness only of each other's bodies and their dual panting breaths.

"I love you," they both whispered. Ten years now since they'd said it first. Still as true as ever. The Doctor met the only things he could see in the dark with his eyes, which were Clara's own, brown and sparkling and just the same as those he'd looked into a decade ago. He pressed a last butterfly kiss to her lips before they snuggled closer to one another and settled down to sleep.

Clara finished her series of six books when she was thirty-eight, and the following year became head of department at her school, still insisting on staying in work, though the Doctor's offers of upping sticks and travelling the universe permanently did seem to tempt her. Clara's fortieth year arrived with typical fanfare, but with one rather unexpected development. A week before her birthday, Clara's optician prescribed her spectacles for general use. She couldn't wear contact lenses, found them hideously uncomfortable, but she was terribly self-conscious about having to wear glasses. The Doctor did his best to reassure her. "You look beautiful," he insisted, quite honestly. "Really."

Clara pouted. Middle age hadn't stopped her ability to throw a good strop. "They look ridiculous. I look like my mum."

To be fair, going off of the pictures she'd shown him, that was a fairly accurate statement. It helped that Clara had adopted a somewhat dowdier fashion in the last couple of years. Still, she was still his beautiful impossible girl. "They don't," he promised. "Really, they suit you."

Clara considered. "Am I…" She thought for a second, then sighed. "Am I getting old?"

The Doctor looked at her. Same brown hair, now tied up, a little less casually than it might once have been. Same lovely figure, though now a little changed by age. Still, it was the eyes he sought out, uncertain and shy behind the offending spectacles that now rimmed them. Same as he remembered. Same girl he'd fallen in love with. Same girl he was still in love with, sixteen years on. "No," he said. "And even if you were, that wouldn't be a bad thing. I'm old, and I'm brilliant."

She giggled. Yep. Still the same girl. "Thanks, Doctor."

From there on Clara wore middle age with a little less self-consciousness. It brought with it a few more pangs of getting older, of course. When she was forty-four her father passed away from stomach cancer. It hurt the Doctor as well- he'd really liked Clara's father; it had been easy to see where she'd got her good humour from, and he'd been terrifically accepting of him. Still, sitting by his bedside, the hardest thing was to see his poor sweet love sitting next to him, sobbing inconsolably, clutching her father's still hand in her own, so hard he'd have cried out in pain if he had the capacity to feel it. The Doctor searched in vain for a way to cheer Clara up in the weeks that followed, but eventually realised he simply had to let her grieve, even if it did cut him up, seeing her so miserable. In the last twenty years his love for her had only grown. They were closer than ever before, and it hurt to see those eyes he'd fallen in love with rimmed red and filled with tears. All he could do was wrap her up in his arms, stroke her hair softly and tell her over and over that he loved her, that one simple truth that was as true now as it had been two decades prior.

After that any self-consciousness Clara had about losing any objective beauty with age seemed to fade. She stopped using hair colour and let her hair go naturally grey, something which in fact suited her well. She stayed gorgeous, in his eyes, though the numbers of fashion magazines looking for her to appear in them did diminish. But she did become happy again, and entered her fifties still with an air of impish good humour that the years couldn't diminish. Aged fifty-two, she earned a telling-off from her boss after the Doctor called in to pick her up from work and she kissed him most enthusiastically, probably traumatising all the students watching on. Goodness knows what they must have thought. Not that either of them cared. Love conquered all, and twenty-eight years on they were as in love as they'd ever been.

Clara took an early retirement aged sixty. It wasn't like she needed any more money. The Doctor did enjoy her being free all of the time, even if things weren't quite as they'd used to be. Their adventures weren't so adventurous anymore- she couldn't do the running they'd used to do, nor the frenetic action they'd used to get up to. Still, her stern demeanour saved more than a few species. On one occasion they stood on the balcony of Kajira's Spire, the tallest structure in the Isop Galaxy which was so high it jutted out into space, looking down on the world they'd just saved. Well, Clara was looking down. The Doctor was looking at her, specifically at her eyes that were taking it all in. They were still the same. She was sixty-four, birthday just gone last week, but those years and the lines on her face couldn't change that fact. She was still his impossible girl.

"Why are you smiling like that?" Clara asked.

The Doctor looked away with false guilt. "Sorry. I'll stop."

A moment's silence passed. "I love you," he said to break it.

"I love you too," came the reply. Forty years on and he still wasn't tired of saying it nor hearing it.

The adventures eventually had to stop. So too did Clara's appearances at all those conventions that wanted her. Even as the years passed she kept active, well into her seventies. Her mind remained razor sharp, and she'd still tease him like when they were younger. Still, everything spoke of the time that had passed. When they looked at old photos together of their adventures, there was no escaping the fact that one of them looked the same, and one of them didn't. Not that that stopped him loving her. For Clara's eightieth birthday he took her to a recital of Queen's Greatest Hits in the fifty-first century, and as ever the joy on her face made his two hearts soar. Still his impossible girl, after all these years.

Then one day looking at the photos stopped working. Clara couldn't remember some of the places, nor some of the people. She was sceptical some of them were even really her. Dread gnawing at the pit of his stomach, he took her to the doctor, a proper one, as she put it. The diagnosis was soon confirmed. At eighty-three, Clara was diagnosed with dementia.

From there, things slowed right down. The Doctor did all he could to keep her mind from going. Every intellectual pursuit to keep her brain as active as possible, he indulged in. But it was no use. Time, that sick psychopath who so loved to watch others suffer, was a force even he couldn't fight sometimes. Every day another piece of her was taken from him. By Clara's eighty-fourth birthday he wondered how many, if any, of the eighty-three prior she remembered.

The days continued to pass. Clara didn't really remember who he was now, but seemed to still harbour a sort of liking for him. She liked his rambling stories about adventures across the stars, about foiling evil and saving planets and doing all sorts of odd things. Her vague smiles at his tales made his chest constrict painfully. He wondered how much more she'd enjoy them if she remembered that it was her in the stories that was doing all of these things.

At last one night he tucked her into bed. It had been a slightly better day today- Clara had been a bit more lucid, which gave him hope that perhaps she might not all be gone yet after all. "I'll be back first thing tomorrow," he promised. "We're going to the park tomorrow. A bit of fresh air might be just the thing."

"That sounds nice." Clara's voice was weak. He remembered once it had been strong and vibrant. Sixty years had passed since she'd asked him that question now.

"Goodnight, Clara." He met her eyes. They stared back, glassy and empty and just a little dazed. They weren't the eyes he remembered. They carried no trace of all those wonderful memories they'd made together. His impossible girl was all but gone. All but gone, and yet he couldn't help loving her all the same. He placed a tender kiss on her forehead, then left.

The next morning he returned in a more positive mood. Overnight he'd convinced himself that he wouldn't be giving up so easily. He owed it to Clara to give her his best efforts, and that meant expecting as much as he could from her. "Clara!" The Doctor called out to her as he entered the house. "We're off to the park, remember?"

Of course you don't, he thought glumly to himself. No, that was negative thinking. There was no room for negative thinking now. He forced a smile onto his face and pushed open her bedroom door. "Still asleep? Come on, Clara, you've got all day to laze around, now we're-"

He reached out to nudge her gently, to wake her up. He froze. Clara was horribly cold. Her face was relaxed, just as it would be in sleep, but her chest did not rise nor fall.

"No!" The Doctor tugged back the covers frantically. Clara didn't react. Somehow he knew she wouldn't. Somewhere in the back of his mind, he knew any resistance was futile. But that wouldn't stop him trying. "Clara! No, you can't, you have to wake up, please-"

But nothing would rouse her. He tried resuscitation, tried rolling her onto her side. In a fit of panicked desperation he simply pulled his sonic screwdriver out and began clicking buttons randomly. But he was powerless. Once more, time had put him back in his place. He who dared call himself a lord of time had been punished for his arrogance. He was no lord. Time could hurt him and he could do absolutely nothing about it.

Many turned out in the end for the funeral of Clara Oswald. Most agreed it was a dreadful thing, but to be expected. She'd lived a good life, a long one, a full one, and had left the world a better place than when she'd entered it. Her old colleagues, her old students, her surviving family members, various writers and actors and producers who'd worked with or around her all came to pay their respects. Many passed remark about the young man who hung around at the back of the church during the service. Some thought they recognised him, though nobody could agree on quite why or how they might have met him. One thing they did agree on, however, was that a bowtie, black or not, was a thoroughly inappropriate choice for a funeral.

So respects were paid and memories were honoured, and then one by one everyone left the graveside, left the church, left the reception hall. Everyone but the Doctor. He was left alone, standing by the headstone in the cemetery. Swallowing, he read the inscription there. Clara Oswald, 1989-2073. A learner and a teacher, and a thoroughly impossible girl.

The Doctor sank slowly to his knees. "Please, Clara," he whispered. "I don't know what to do on my own. Please give me something. Anything. I'm so lost…"

No reply came. Pitifully and pathetically, the Doctor began to cry. It seemed to go on forever, and with nothing to stem the tide he just had to let the teardrops fall onto the ground below. He held onto the headstone for support, cheek pressed against the cold stone, as if somehow this could make up for the fact that he'd never again hold the one it was for in his arms again. "I'm so lonely," he said to himself. And he was. After everything, all he'd done in his life, this was where he'd ended up. Alone, on his knees, crying in a graveyard over the plot of a dead woman, utterly helpless and utterly hopeless. Was this really what his life had led up to?

"I'm so lonely," he repeated. He was absolutely alone. He had nobody. The last person in his life that had truly understood him was gone. What was he supposed to do now?

The answer came to him after much thought. Resignedly, the Doctor got to his feet. He bade farewell to the stone that marked Clara's grave, and made his way wearily to the TARDIS. Maybe there was just one little thing left for him to cling to in his life. This funny little blue box with all its wonders inside. It just wasn't worth it, though. Not anymore. Not if this hurt was all he had left to live with.

But now he was ready. Ready to do what he'd been putting off for a long, long time. "Come on then, old girl," he said, patting the console fondly. "One last trip, eh?"

He set the coordinates. At long last, he would return to Trenzalore. It was high time he faced up to his fate. He'd been running for far too long. And now, at least, if there was an 'other side,' he had someone on it there waiting for him.

He pulled a lever. The familiar roar of the TARDIS swelled up round him. Off he went, then. At long last, he could stop running. Maybe there would be an 'other side,' maybe there wouldn't be. Some things didn't die, though. He'd promised to love Clara forever, and the Doctor kept his promises.