Twilight blinked. What had happened to the colt she thought she knew so well? Well, better than any other pony would, anyway.
"So how do I look?" The Doctor asked, smiling.
Twilight scrutinized him. Out of the changes that had happened, the most obvious one was that his horn was gone; it had disappeared! He was know . . . an Earth pony! Not looking awfully bad in the Doctor's jacket . . . or his jacket, if it was true that he was the same colt, that is. But seeing that he had a lighter complextion, a very speedily grown mane, and . . . slightly thinner? No, wait . . . this wasn't possible. He couldn't be the same pony . . . no.
"Well . . ." Twilight started to speak.
"Wait, wait wait wait wait wait wait!" he exclaimed. "Don't tell me . . ." With a grin as wide as a mile, he ruffled his body with his hooves.
"Oh, big hair! And . . ." he gulped. "The new teeth . . . those still get to me . . . say, the jacket doesn't look so bad . . . but a waistcoat . . . yes, that would fit very nicely. Going to have to get straight to the wardrobe once we land. Wait a minute . . . I've got a sideburn! Ha! Didn't know that was possible here . . . should I call it a maneburn?
Twilight almost rolled her eyes. The real Doctor had always had been manic and garrulous, but here was this colt, looking like someone who had never set a hoof on the earth.
"Oh . . . oh!" he said, flexing his right front leg. "This may interest you Twilight: I seem to have a small weakness in my dorsal tubercle; a module found in the foreleg. There's some knowlodge to add to what you already know on pony anatomy. Or did you know that already? Wouldn't be surprised to hear that from your mouth. And my skin tone . . ."
Twilight couldn't help herself. "YOU'RE NOT THE DOCTOR!" she shouted. "You're, you're an imposter; a different pony!" She was angry at the colt now, trying to impersonate the Doctor. Trying to fool her into thinking he had changed his physical form . . .
The Doctor himself was rather shocked by her sudden outlash, along with her doubt of him. "Twilight, I changed right in front of you! You know, big lights, my bouts of pain; regeneration? I'm him . . . the Doctor! I'm the Doctor!"
She shook her head. "No, I've seen the Reapers; they can change their form. Now bring the Doctor back!" No, she wouldn't be so easily fooled by anypony into thinking that the Doctor was completely safe beside her, while he was actually kept prisoner. She would never be rid of that notion.
Rather not wanting to have the prospect of an angry (not to mention stubborn) Twilight against him, the Doctor tried to reminisce about all their past adventures. "Don't get mad at me, Twilight!" he replied quickly. "Yeah, I have a new face and all, different body- and a sideburn?" the Doctor felt the sides of his head. "Yes, I forgot about that for a second. But it really is the same old me, you see? Your Doctor." He knew he looked at least similar to his previous form somewhat. "And- and I remember how we first met! You know, with the Nestene Ponyquinns in March?"
Twilight felt less confused now, but still looked at the (so-called) Doctor with suspicion. It could still be a intricate trap to snare both her and the Doctor, along with the TARDIS. She began once more. "Do you really remember . . . -remember being . . . him? The Doctor?"
He rapidly nodded. "Of course! Oh, and the hopping- that stuff! Do you recall that, Twilight? Hop, hop, hoppity-hoof, hopping for our lives? That was rather something, wasn't it? And the Equestrian Blitz, with Captain Jack, and the Slitheen, running on Downing Street?!" he spoke with growing enthusiasm. "Yes, it really is me! Oh, and-"
Twilight didn't hear the rest as her eyes welled up with tears, thinking of all the moments they had shared. Mayor Mare, overweight with a zipper on her forehead, and the Daleks on Satellite Five. Platform One, end of the world, and Starswirled the Bearded. The empty filly, with the gas mask. The words "Diamond Dog", scattered across the spacetime continuum. The tears now streaked her face, falling to the grating with a tiny splash. After several moments, she interrupted him.
"Can you change back?" she asked softly.
The Doctor stopped his rabble abruptly. He bowed his head, and turned it to face her, with the face of an old colt; sad and dark.
Slowly, he responded. "Do you want me to?"
Almost imperceptibly, she nodded, too overwhelmed for speech.
"Well . . . I can't. I . . . I'm . . ." he paused for a while. "I can't go back. And I truly am sorry."
Twilight stayed silent for the next several minutes, with the only audible sound being the groaning engine of the TARDIS, and the new Doctor going around the console, flipping various controls, as if testing what each one did.
Eventually, he spoke up. "You loved that colt, didn't you?"
Twilight nodded again, this time parched, the tears having dried her out.
The Doctor nodded back.
Suddenly, the Doctor kneeled forward, shouting in pain. Grasping at his stomach, he gasped for air, immobilized on the floor.
Twilight hurried over, with a look of alarm. "Doctor . . . are you all right? Doctor?!"
He looked up at her. "Post-regenerative stress." he barely said. "Having quite a fit here; adjusting to this new body of mine."
Twilight concluded that his response meant "No."
After a few moments, he managed to stand back up, falling several times before being able to erect himself on all fours. "Well, then." The Doctor said, having some minor difficulty breathing. "Would you like to go back?" he asked. "I mean, really, it's your choice and all. Would you like to go back to Canterlot; home sweet home?"
Twilight didn't reply. In truth, she imagined that she would travel with the Doctor forever, flying amongst the stars, going to new places everyday. She never really gave any thought to the possibility that she would have to go back to her quite regular, mundane life at home, even after the Doctor had tried to make her do so, leaving the TARDIS to die. In fact, her return made her think all the more that nothing could keep them apart, no matter the true distance that separated the two, whether related to time or space. Keeping silent, she pointed her head down at the hexagonal pattern that latticed the grating around the console room.
Not getting an answer, the Doctor stepped up to the controls and started to fire at them, as he ressurected all his former memories of flying the thing, pressing buttons and flipping switches.
"Equestria, Canterlot . . . Chariot Street, the Celestial Estate . . . December the 24th, 10'o'clock A.M.- your home!" he exclaimed, smiling at Twilight. The groans of the engine became louder, and the ground shook as the space ship took flight. "Consider it a Hearthwarmer's Eve present."
She smiled back.