December 25, 2005 (During Christmas Invasion)
"You told me I was going to have a great year."
Rose had been drinking in the Doctor's new face when she remembered it.
"What?" He took off his glasses—he'd been reading Je Veux Ma Banane, some French children's tale about bananas ("It's handy to be multicultural, Rose. Never know when a French ambassador will require a banana. Bananas, great fruit they are…" the Doctor had prattled on about bananas and the time he switched Jack's Sonic Blaster with a banana for the next hour or so).
"January the first. You told me I was gonna have a great year."
"No I didn't."
"But you did! Day one of the best year of my life, and you were there. I was walking home and I heard a noise behind me—it was you. I asked, 'Are you alright, mate?' You said 'yeah.' I asked if you had too much to drink. 'Something like that,' you told me. I suggested maybe it was time for you to go home, wished you a happy new year. 'What year is this?' you asked me. I remember that bit especially—'Blimey,' I said, 'how much have you'—"
"1986 was a pretty good year for me." The Doctor had a faraway look on his face.
"Why? What happened in 1986?" Rose asked, now distracted from her point. The Doctor just looked at her. "That's the year I was born," Rose said nonchalantly.
"I know."
Rose now felt uncomfortable under his gaze.
"What happened that night is your past. My future. I don't know why I would go back in time to see you, but I do know—" He stopped. It must be bad. Very bad, he had been about to say.
"What?" Rose asked after a beat of silence.
"Drop it," he said, returning to his book. He hadn't even bothered to put his glasses back on.
She dropped the conversation, but her mind was stuck on the subject.
So the Doctor, Mickey, Jackie and Rose celebrated Christmas together. Rose had to admit, it was a pretty great day. She got the Doctor back after she thought she had lost him, saved the Earth from an alien invasion, and now the three people she loved most in the universe were laughing together, safe and sound.
They embraced a new year together, and soon the Doctor and Rose were off wandering the stars again.
Rose often thought of the stranger on New Year's Day—she thought about bringing it up (quite frequently) to the Doctor, but decided that one day she'd just find out the story behind it.
July 14, 2006 (Shortly after Doomsday)
Rose was stuck in a parallel universe.
Meanwhile, the Doctor was probably flying through time and space with a new companion, a new woman.
Rose, who sulked about quite a lot these days, would never know the truth behind the stranger on New Year's Day. Though she did have some theories: maybe he missed her after their departure, ached for her like she ached for him. Though he, with the capability of going back in time to see her again, did just that.
Or maybe he was dying.
June 28, 2008 (During The Stolen Earth and Journey's End)
He had not been dying. But he was now.
She found him, and he found her. They were running (for when were they not?), and tears of joy had been turned into tears of despair—
false alarm.
Epilogue
He left her there with him. A human Doctor, a forever Doctor. She was happy in his arms now, though, because she came to realize that he was in fact, the Doctor. Her Doctor.
She hadn't forgotten the stranger on New Year's Day, not quite—more like she'd forgotten the importance of the stranger on New Year's Day. Though he never forgot her, or her importance. Even with a new (or if you want to get technical, a new new new new new new new new new new new) face.
She got her happy ending, and that is what matters, he reminds himself.