Donna, as it turned out, had a much better idea. An idea that didn't involve having her memories taken from her and having to go back to watching TV shows about minor celebrities being made to live together in an earthquake zone. (Though to be honest he thought I'm A Celebrity, Stop The Plate Tectonics! was quite enjoyable for what it was.)
The much better idea involved rewiring the Chameleon Arch to turn her into a Time Lord, memory mostly intact. "Mostly" because he wasn't keen on her knowing all his secrets, like his real name or the details of his childhood or about that time he'd completely failed to shag Tegan despite his best efforts. There were things that Donna didn't need to know, put it that way.
Obviously he hadn't thought of this himself because he didn't want to force her to change species. It wasn't because Donna with his brain was cleverer than he was. It couldn't possibly be that.
So Donna was now a Time Lord.
The Doctor felt terribly upset about the loss of her humanity, but Donna didn't seem fussed. She'd spent quite some time listening to her new hearts, prodding herself and smiling at the TARDIS, before disappearing into the depths of the machine to "check out the bits I don't want you knowing about."
Gallifreyan genetic engineering had done some amazing things with the female reproductive system, and Donna had effectively asked him not to think about pink elephants. He did lo... like Donna, but sometimes she dragged things down to levels he tried to pretend not to know anything about.
Still, it would all work out in the end.
He had, of course, travelled with another Time Lord before. It occurred to him only now that he'd retconned a lot of it in his head so that his time with Romana had mostly been about laughing at clever jokes, being brilliant together, and having fantastic Time Lord sex.
He'd forgotten that not being the only Time Lord made him feel a bit less special.
His ego hurt as he followed Donna back to the TARDIS.
"Right," she said, "that's two planets I've saved this week, and you haven't even managed one. That means I'm ahead of you by four this month, because we agreed not to count that one where you did it by accident."
"It's not a competition!" he whined.
"Yes, it is, Spaceman. A competition that I'm winning."
"And I don't think you get to call me Spaceman when you're a Time Lord yourself now."
Donna stopped and turned to look at him. "Yeah, but I'm sort of half-Human, and you're not."
Yep, really glad he hadn't let her keep his memories.
"Besides," she continued, "I need to call you something."
"What's wrong with 'Doctor'?"
"That implies a certain respect that I don't always feel. What am I supposed to call you when you're being a twat?"
And it was a lot harder to get away with being a wanker when she knew it wasn't just An Alien Thing.
"I remember when you looked up to me," he sulked.
"Only because you're taller than I am." She smiled an annoying smile. "I love being a Time Lord. I'm really good at it."
She was. She was infuriatingly good at it. She'd built her own sonic screwdriver and a sonic other thing that he wasn't supposed to know about. Both of them had more settings than his own, now sadly less impressive, device.
"You're shit at time-sensitive grammar," he said, without quite meaning to.
Donna waved a hand. "Oh, who cares about that? I'm good at the stuff that matters." She turned back towards the TARDIS.
The Doctor insulted her parentage in Venusian.
"I heard that."
"And so I when I finally managed to find the chameleon circuit, it was all covered in... are you looking at my tits?"
The Doctor snapped out of his reverie and moved his gaze upwards. "No! I was just staring into space. It's not my fault if your breasts were in the way."
"So you were staring at my tits and you weren't listening to me?"
It was a close thing, but he decided that not listening to her would annoy her more than the other bit. "Donna, they're very... they cover quite a lot of your upper body."
"That's your excuse? That they're too big not stare at like a small boy a sweet-shop window? And there I was thinking you're a feminist!"
"I can be a feminist and still appreciate a nice pair of tits!" Shit, had he actually said that?
Donna threw her hands up. "I knew this would happen! I knew you'd want to mate with me!"
"I don't want to mate with you! I was only looking! I look at lots of things, that doesn't mean I want to have babies with them!"
"Don't pretend that me being a Time Lord hasn't ramped up our sexual tension."
"What sexual tension?" Feigning ignorance was worth a try, surely?
"The tension I felt in your trousers when you fell on top of me last week?"
"That was my sonic screwdriver!"
"So you said!" She poked him in the chest. "You're all phermones and lusty glances. Don't think I haven't noticed. You've probably picked out names for the babies."
How could she possibly know that? "Don't talk bollocks!" he retorted, a bit too loudly. "I think of you as sexless!"
"What about my boobs?"
"Apart from your breasts!"
Donna snorted. "If you so much as think about shagging me, I'm going to cut your balls off while you're asleep." She turned some dials on the console.
"What are you doing?" He didn't want to move round to look in case he brushed against her and had sexual tension.
"Taking you to visit River Song. She can deal with your hormones, the randy cow."
"She's not a randy cow!"
"Whatever, I just didn't want to call her your girlfriend in case you went on for half an hour about how she isn't. Rivers in Egypt, Doctor, have nothing on you."
"You were much nicer as a Human."
"That was before you were desperate to get into my knickers."
He was, yet again, really glad he hadn't let her keep his more personal memories.
The Doctor tossed and turned in his bed, trying not to think about sex. It was really, really difficult.
"Look," he said to the ceiling, "she's arrogant, and annoying, and she thinks she's so much cleverer than me. She's not my type."
He imagined Donna smirking at him, which might have helped a bit if she hadn't been naked.
"Yes," he told the room, "she's kind and brave and intelligent and ginger, but what's that against her many faults? Anyway, she doesn't like me anymore. She's not as easily impressed and that's made her notice my personality. Which is amazingly shallow of her, and I don't find that sexy."
But he did. Oh, he did. Now she had an amazing brain to match her amazing breasts, and the combination was getting a bit much. He didn't like having to wank frantically after arguments and having to grip the fixtures to avoid touching her. It was all too much. He would go insane. How could anyone be expected to cope with this?
Maybe she'd shag him if he asked nicely and promised never to mention it ever again?
He had, stupidly, explained the situation to River, who said she'd be up for a threesome. Couldn't she at least be jealous? He never thought he'd be wishing for enforced monogamy, but it would be nice to have another excuse not to have sex with Donna.
"Bloody hell," he said, and reached for his cock. At least wanking himself to sleep while feeling miserable was something he was used to. It was oddly comforting.
Almost inevitably, the Doctor's unrequited shag soon blossomed into unrequited love. Luckily he had never been entirely clear on the difference between loving someone and being "in" love with someone, so Donna didn't think anything was up when he told her how wonderful she was or grinned at her like an idiot.
At least she wouldn't die on him, and she seemed to have no plans to leave. It could last forever, giving him something to replace the misery of being the last of his kind. He needed a bit of misery, so that he didn't feel shallow.
By this point he'd shagged way more humans than Time Lords. It wasn't pervy alien-fancying, honest, just that he didn't have as much opportunity with Time Lords. And he hadn't really had that much luck with the Time Lords he'd got into bed with. The Master had gone evil, Romana had left N-Space to get away from him (and had possibly turned into a bit of a furry), his wife had decided to die just to see what it was like, and... well, he'd only shagged the Rani once, and she hadn't even let him come. So you couldn't blame him for that one. But generally he hadn't had much luck with his own species.
But, of course, it would be different with Donna.
The Doctor decided not to think about how many times he'd used the phrase "it'll be different this time" about companions and/or lovers.
"What's this for?" asked Donna when he presented her with a bunch of flowers that he'd picked from the meadows outside the TARDIS.
"For being you," he said with a soppy grin. The seduction of Donna Noble was going, he felt, really well. Soon she would love him almost as much as he loved her.
"What is it with you and flowers these days?" She found a vase and stuck the bouquet into it rather carelessly. "At least these ones don't have teeth."
"That was a mistake anyone could have made." Besides, it hadn't worked out too badly. He felt sure they had bonded romantically while beating those particular plants to death with hammers.
"Men don't usually get me flowers unless they're trying to get me into bed."
"Um," said the Doctor.
"At least I know you're not doing it to seduce me. Let's face it, you're a bit crap at that sort of thing."
"I'm not!" Was that giving too much away?
"You are a bit. You just stand there and wait for people to jump on top of you."
"I think you're simplifying my sexuality a bit too much."
Donna shrugged. "I try not to give too much thought to your sexuality."
"I know," he said, sadly.
"Anyway, thanks for the flowers."
"I'll just go and have a shower," he said, and went off for a quick wank.
"Bloody sex pollen," said Donna as she dragged him into her bedroom.
"I really am sorry," he told her, pulling his feet from his shoes.
"Yeah, well, this'll teach you to be careful when you're picking weird flowers to give to people." Donna pushed him onto her bed and started to wriggle out of her dress.
"This wouldn't be happening if we didn't already have sexual tension," he said, trying to get his trousers off.
"It's your fault for being in love with me." She chucked her dress into a corner and kicked off her shoes.
"What? I'm... I'm not in love with you!"
"I don't mind, it's sort of cute. Just don't think I'm going to marry you after this."
"But we're the only Time Lords in the universe!" He struggled to get his shirt off, which had way too many buttons on it.
"You'd better not cry while we're shagging," she said, climbing on top of him.
Still, having shagged once there wasn't really much reason not to do it whenever the sexual tension got too distracting. He loved her, she didn't hate him, and they had sex occasionally. It was a bit like being married but without the terror of commitment.
"I like our relationship," he told her.
"I think we've struck a good balance," she agreed.
"You're still not in love with me, are you?"
"Never gonna happen, Spaceman."
"It's okay, I sort of enjoy the angst." The Doctor smiled to himself and went back to working out how to make her fall in love with him. She'd come round eventually.
And they all lived happily ever after. More or less. Sort of. It's probably best not to think about it.