Timeline/setting: S6, while Eleven was on his farewell tour. 2059 London.
The Doctor steps out of the TARDIS, on yet another farewell tour. This time he's landed in London, a bit later than intended. He's surprised when the first person he comes across appears to be Donna.
He fixes his bow tie before approaching her, knowing he can talk to her without her remembering who she is, "Hi! You must be Donna Noble…"
"No." The woman cuts him off, suddenly looking very sad, "That's my mum. She died yesterday, age 80. Who are you?"
"Oh, I'm nobody… Just an old friend…" He frowns, not understanding, "I'm sorry… What year is this?"
"It's 2059… Why?" She asks, utterly confused, then it hits her, "You're him, aren't you? The man my great grandpa Wilf told me stories about when I was little… He always told me to not tell mum."
The Doctor smiled a little, he should have known Wilf wouldn't let the memory of him die, "Yeah, I suppose I am. Sorry for your loss."
The woman smiles slightly, "Wilf said so many great things about you, you know. Why wasn't my mum allowed to know?"
"Sorry… Can't really say." He turns around, smiling widely as an idea comes to him then turns back to Donna's daughter, "You wouldn't happen to know the time she died yesterday. And where?"
"It was about 7:14 in the morning, at the senior's home down the road. Why?"
"She forgot because she had to. Otherwise she would have died. About me and everything we ever did." He finally answers, looking away, "She should have those memories back before she dies. They are too important. She is too important."
The woman nods, smiling as she understands.
"By the way, what's your name? I never got it." He asks before leaving.
"Jenny." She answers, "Jenny Temple."
He smiles, realizing Donna subconsciously must have remembered Jenny. "Goodbye, Jenny."
"Bye, Doctor." She waves at him as he turns away, then stops him, "Doctor?"
He turns to face her again, she's like her mum, isn't she, "Yes?"
"Will I ever see you again?"
"If I'm lucky." He answers with a smirk before turning away and returning to his TARDIS.
Once the Doctor is back in the TARDIS, he runs over to the console and sets the coordinates and materializes in the previous day, same place, about thirty minutes before the death of Donna Noble.
He exits, walking into the senior's home. A nurse immediately comes to help him, "Can I help you, sir?"
"Yes. I'm looking for Donna Noble? I'm an old friend."
"Oh, I'm sorry. She's not doing well…"
"Can I see her? Please?"
The nurse nods and leads him to Donna's room. He walks in, surprised to see she's awake, "Hello, Donna Noble."
"Hello… I'm sorry, do I know you?" She asks, sounding exhausted.
"Yes, I'm an old friend…" The Doctor smiles, willing himself to not cry, "Well, I used to be. I was a different man, back then."
Donna chuckles softly, "You make no sense."
"Oh, Donna Noble… You are brilliant, you know that? Absolutely magnificent."
"I'm not, really." She counters with a tired smile, "I've done nothing in my life, I've been so unimportant. I was nobody."
"Oh, you were somebody to me. A very important somebody." He counters with a weak smile, looking at the time and realizing she only has five minutes left, "And now, it's about time you realize that." He adds as he leans over her, holding the sides of her face like he did all those years ago, this time to give her back her long lost memories.
Donna's time spent with the Doctor flashed before her eyes as she remembered every moment. "I always felt like I was missing something…" She says, a single, happy tear sliding down her cheek.
"Well, now you don't have to miss anything, my brilliant Donna Noble." The Doctor replies with a smile.
"Doctor…" She murmurs, smiling. And with that, she dies peacefully. Complete.