"I will kill River- no, better. I will torture her and then kill her." The Eleventh Doctor said, angry that he was trapped on Earth because River fancied a trip and left him there.
She thought he deserved the punishment, but he could see right through her; this was something future-him told past-her to do. "Bloody spoilers," he spat.
And as he was walking down one of those streets in London that could be any other street in the world, he saw her sitting in a restaurant.
When he left Donna Noble on that rainy day oh so long ago, and saw her at her wedding, everything hurt. It was one more goodbye, one more burst of pain building up to break him; but it was by far one of the hardest blows to his old hearts.
She looked skinnier- which made him mad because she was in perfectly lovely shape when he left her. How dare she?
And just then he spotted a little girl sitting at the same table as her. Dark curly hair, which he thought was a pity with that available and perfectly perfect ginger gene she carried, but the girl's eyes told him everything. The y were same shade and shape as Donna's, with that mesmerizing golden circle. He must have looked like a nutter, staring at them from the other side of the large window on the side of the restaurant- however he was never one to care about such matters.
He remembered the Library, and how it hurt her to lose the children CAL gave her. And how she felt the clock ticking and her chances diming but never said a thing, not really- he just knew; the sacrifices she made to be with him and how willing she was to give forever.
And oh boy, how he had believed it.
She looked so absolutely happy, laughing at her daughter's antics, trying to make her eat one thing or another, that it took his breath away.
He knew she probably went through what he had seen in Amy when Rory got caught in the crack; crying and not knowing why, missing something she wasn't sure of, something mysterious and unknown. But oh, she had overcome it. Beautifully.
For the first time since that dreadful day, the day that made him cringe every time someone asked about the Chameleon circuit, he didn't feel so guilty or so sorry for both of them. He wasn't so sorry about the woman he'd left behind.
At that moment he felt a hand against his.
"Sorry, love, you had to see this. You told me so yourself."
"Future-me is very clever, oh so clever. I really did need to see this."
"The good in goodbye."
"What?"
"That's what you called her, the good in goodbye. Who is she, Doctor?"
"Donna Noble, River you should've seen her shine -she was… she was a Force of Nature. So very human."
River made mental notes to never forget that name- she never knew what she would need if she was ever going to find a past version of her Doctor; she needed those names. And she definitely needed to remember that one, she knew it from the look on his face.
They walked hand in hand back to the TARDIS and The Doctor stole one last glance of his old companion. Maybe there was a good in goodbye after all.
He heard River whisper, "The one he never forgot."
Something clicked inside him. His wife back in Gallifrey was the one for whom he would do everything again; Rose was the one he gave a part of himself to; River was the one he married; and Donna, brilliant and extremely important Donna, was the one he never forgot. From the way River said those words, he knew it was a fact that not even time or regeneration changed his thoughts of Donna. After all, someone had to remember 'Forever'.