After dropping Amy and Rory off on a honeymoon planet for their honeymoon, the Doctor decided that he also deserved a little relaxation. So, he landed the TARDIS in 2019, right outside a little shop in Cardiff and bought himself a newly released copy of the eighth Harry Potter novel. He'd been anxious to catch up with good 'ol JK for awhile now.
He set the TARDIS to drift calmly throughout space, and then settled in for a read, lying down on the console room floor. He was a few chapters in and starting to seriously ponder if the Master might have something similar to horcruxes, when he caught a moving glimmer out of the corner of his eye. He glanced fully up, and saw a man...standing in his TARDIS...in what looked like a sharp tuxedo. "WHAT?" He took a moment to place a bookmark on the page, and then stood up, sonic screwdriver in hand.
The stranger turned around and flashed him a cheeky grin. "WHAT?!" he exclaimed, mockingly. "WHAT."
The Doctor stumbled back, nearly chocking.
But the man just winked. "Ahhh, the shock of a wedding participant materializing inside the TARDIS - good times! Brilliant, in fact.”
The Doctor ran a hand through his own long hair. With the stranger's sticky-uppity hair, dimples and expressive eyebrows, he wasn’t a stranger at all. He even wore a bow tie. But the mere fact that he was here - presently present inside the TARDIS - couldn't be, well - stranger. Throwing the sonic screwdriver down, the Doctor leapt over to the man and pried open his left eyelid - the hell with personal space. "You must be sick. Or I - I must be sick. We must be sick. I feel fine though. Are you sick?"
"Wellllll, I did just eat a banana, and now I feel a tinsy bit constipated. But I think it'll pass soon enough." He pat his stomach. "Thanks for asking!"
The Doctor pried upon the man's mouth. Yes, there was a whiff of banana. "But I don't remember this happening before. When I, I mean - when we - collided the TARDISes on her own timeline before, I remembered. This event is brand new. And I closed the cracks in the universe, so that doesn't explain this either."
The strange not-so-stranger stranger raised an eyebrow and put his hands in his pockets. "Who do you think I am?" He asked coolly.
"What exactly do you mean? I don't just think about who you are. I know who you are. You're me. I know you're me. Of course you're me. But how can you be me...when the me that is currently me doesn't remember this happening to me when I was you?"
The man stood on his tiptoes. "Ohhh well, that's easy. I'm not you. Wellll…not really anyway."
The Doctor leaned in even closer. "Cassandra?"
"What?!" The man sounded genuinely insulted. "No. Don’t be so thick. Guess again."
The Doctor grabbed a hold of the man’s face with both hands. "Why don't you seem the least bit surprised to be here - almost like you expected it? Why aren’t you intrigued — or at all interested really - by my new appearance? And why, dear goodness why, would you bother to wear a bow tie that is just plain old boring black? Bow ties are very cool, but red, green or blue bow ties are even cooler. Why don't you know that yet?" He let go of the man’s face, but continued to stare.
"Ahhh! Brilliant questions. I knew they would be." The man placed his own hands tightly on the Doctor's shoulder. "One - I planned to be here. Two - I knew exactly what you looked like, hipster gramps. And four — no wait, three - I'm going to a wedding and the attire is called 'black tie' not; ‘any color of the rainbow tie'." Oh and in case those answers didn't help, here's another hint:” He paused for a moment and guided the Doctor’s fingers to his own chest. "This is my heart. My only one.”
The Doctor jerked his hand back and starred at the man before him, suddenly seeing him in a whole new light.
The man had on a huge grin. "Yup, yup, I see that big old brain of yours working. Welllll, I can’t see your brain actually. It's only a matter a speech - very human. In fact --"
The Doctor put a hand up, silencing him. "Human-Time Lord metacrisis?"
"Hello!" said the man, waving his right hand. "But you, old man, may call me ‘the Doctor’.” He winked.
The original Doctor was still terribly confused. "But, but, but....how did you get here? You don't even live in the same universe? This shouldn't --"
But the half-human Doctor wasn’t listening. He had run over and seized the Harry Potter book.
"Oh, brilliant! I've wanted to read this for ages!" He began to flip through the pages and didn't take his eyes off it. "I knew it would eventually be published of course, but since you abandoned me without a TARDIS, I haven't been able to get my hands on it. Not even with our magical handy spare hand."
"Doctor , I --"
The half-human spun back around. "Tell me -- is Barty Crouch Junior by chance in it at all? I loved that character…especially in the films. Or was it just one film he was featured in? I forget now..."
The Doctor shook his head, ran up to the not-him and slapped him hard across the face. "God, I forgot how much you could ramble."
The other fell back. "What was that for?!"
"...And how squeaky your voice could get."
“Well, you- you —“ The half-human pointed a finger at the Doctor as he tried to stand fully back up. “You…STILL AREN’T GINGER!”
The Doctor tried to think up a witty retort, but just shook his head. Never mind silly insults. He had more pressing matters to attend to. “Okay, besides how you got here, you said that you actually planned to be here. Why? Is something wrong?”
“Ahh no! Me wearing this cheeky smile when there’s danger? No no. This is a happy call. No big bad wolf. Don't you worry your big new forehead off.” The half-human pulled several TARDIS controls and the whole machine lurched forward. “I’ll show you why I’m here. Allonsy!”
“It’s ‘Geronimo.’ I say ‘Geronimo’ now.” The Doctor bent down and grabbed a box that was set next to the Harry Potter book — a dozen biscuits that he bought earlier at the shop. If this was truly just a fun trip, (and why should he doubt his somewhat-cloned-self?) he figured that he could relax a little and enjoy a snack.“Biscuit?" He offered one to his latest companion. "You really should eat one or two....or twenty. Goodness, I nearly forgot how skinny you are. Donna was right.”
“Oh right. Good ‘ol Donna. You’ll see her in a minute.”
The Doctor felt his hearts skip a beat. “But Donna can’t know!” He yanked the half-human forward by his bow tie. “My goodness, you really must be sick. What kind of sodding idiot have you become?”
“Oi, watch it Time Lord!” He snapped the Doctor’s bow tie. “I’m no idiot. Just think for a minute, will ya? We’re not going to see your Donna Noble — we’re going to see -”
"Your world's." The Doctor slowly nodded and released his grasp on the other man. Right, that made sense. Of course his half-human self would want to befriend his best mate — even if she wasn’t truly the same woman.
“Oh and did I mention a certain Miss Tyler who’s expecting you too?” The half-human Doctor smiled broadly as the TARDIS landed.