A/N: I shamelessly broke canon, but ignoring that, most of this seems relatively plausible. Liz was the companion during the 1970 season, so we'll say that the events take place in 1970 as well, making Kate 45. Jemma Redgrave looks 45, no? Anyway, enjoy. Liz/Brig is never appreciated in my opinion, so there you have it. Takes place at the end of Day of the Doctor.
All in a day's work, he thought.
Saving the world, his world this time, side by side with UNIT. It reminds him so much of the old days, the long-gone old days of exile and return and friends he will never forget.
It pained him more than he will ever admit to himself when he found out that the Brigadier had died. He had always seemed to be there, regeneration after regeneration, the straight-backed and dry soldier.
But now the torch has been passed to his daughter.
He hopes to see her again, to have her help again.
Like the old days.
"Your father would have been proud," he says, without turning around from where he is admiring the painting that is the answer to everything.
Kate Lethbridge-Stewart walks so she stands next to him and smiles, a sad smile full of nostalgia for the man they both remember so well.
"Your mother, too," the Doctor continues, glancing sideways at Kate.
"Yes, you knew her as well, didn't you," she replies, meeting his slightly questioning gaze. "Dr. Elisabeth Shaw."
He was right then, he had guessed it long before but was never sure.
"Liz," he say wistfully. "Yes, I knew her. Absolutely brilliant woman, wonderful person, too. Could scold me like no one else. I always had a feeling your dad fancied her."
Kate smiles at that.
"He was so in love with her. Well, as much as he could be. He was never one for displaying affection."
The Doctor grins hearing her say that.
"I was born after she left you, and they got married when I was twelve. I grew up hearing so much about you. From both of them. And she forgave you, you know."
"Yes, well, I never seemed to give Liz her due. It took me too long to recognize how much of a genius she really was. Always made her pass test tubes, or some nonsense. She was more of an equal to me than I ever realized." He pauses, and then says it, because he has to. "Is she, is she still..."
"No."
"God, I'm so sorry."
"It's perfectly alright, Doctor. She always made a point of living her life as she wanted to. She stayed on at Cambridge for years, and came back to UNIT several times as well. She died just before Dad, so they were never apart."
The Doctor glances up at her again, glimpsing the smallest tear escape her eye.
"You remind me so much of her, you know. When I met you, it was like having the Brigadier and Liz by my side all over again. They have an amazing legacy in you, Kate Lethbridge-Stewart."
He leaves her then, leaves her knowing without exchanging a word how much what he has said means.