A/N: The Doctor having to tell Amy and Rory about River's death is something that angst happy me became fascinated with the moment I found out she was their daughter. And then...he never really could. I also see Darillium/experiencing River's death the second time as the real "end" to the Pond/Williams/River era. Eleven taking River to Darillium in the Night and the Doctor features makes this the teensiest bit AU, I guess, but I wanted some time to pass because of reasons.
"I do not say goodbye. I believe that's one of the bullshitiest words ever invented. It's not like you're given the choice to say bad-bye, or awful-bye, or couldn't-care-less-about-you-bye. Everytime you leave, it's supposed to be a good one."-Will Grayson, Will Grayson by John Green and David Levithan
It didn't fully hit him until years after they had stopped travelling with him, long after he had regenerated and put away the tweed jackets, braces, and bow ties (for now). Honestly, the thought wasn't on his mind while he was at Darrilium or during the days of what can only be described as moping that followed.
A week, later, however, the TARDIS became impatient and started humming louder than usual in an effort to pull him back into his routine of saving the universe and such. The Doctor rolled his eyes and told her to mind her own business before walking into the kitchen... or what used to be the kitchen before he offended his ship and was now just an empty room. It took two apologies to get his kitchen back. By then, his mood had soured more, causing tea making to be a noisy and aggressive activity. When he reached for a mug, the TARDIS successfully won this battle: the Doctor stared numbly at Amy's old mug for a moment before muttering "Ponds" under his breath. He sighed and made his way to the library.
The Doctor had planned on telling them in person, he honestly did. He didn't want his best friends to be waiting for forever for the next visit or letter from their daughter that never came, with no explanation. River wouldn't know to prepare a goodbye, or did not know, past tense, and it wasn't like that was her responsibility anyway. It was his job to tell them, somehow, that he was responsible for Amy and Rory losing their daughter and friend Melody Pond, River Song… again.
Only, now the TARDIS couldn't go close enough to them for a visit. He would never see them in person again. He knew he had their addresses by year somewhere, because River used to tease him about how useful old-fashioned mail could be, but writing a letter felt so…So probably not the best way to tell your friends that someone they love has died. Bit rude, even for him, when he's sulking and feeling guilty. Maybe…
An hour later, he walked to the control room and pushed a button on the console.
"Hello, Ponds! I look awfully handsome with this face, I know," he forced the biggest smile he could, for them, "I hope you're not causing too much trouble in America. I…" Oh, this was not going well at all. The Doctor took off the reading glasses he technically didn't need for reasons other than looking smarter than he already did. "You remember how my time line works with River's? I would hope so, even though you're, well," he crinkled his nose at the thought, "extremely old. Oooh, that was rude, wasn't it? Sorry. Anyway, if I do this right, River will have gone to visit you pre-Library at my suggestion a few weeks ago at most. I never told you the whole story about when I first met River, because it was spoilers. But, you'd be so proud Rory the Roman and Amelia Pond. She was so brave. I was still in my Tenth body, bit before I crashed and met you…"
Several stories and far too many humany wumany tears, both happy and sad, later, the Doctor was satisfied. The video was put onto DVD, the DVD and a portable DVD player placed into a box, and a note placed in the top.
Dear Ponds,
First of all, don't panic, it's just regeneration, still me...Who am I kidding, not quite as traumatic as watching one in Hitler's office. Just a face change. Second, do remember to hide the DVD player well so you don't cause a paradox. Third, I am so so sorry.
The Doctor
Longer attempts at a note had failed and that one at least…got the main points across. A month later, he guiltily crammed their favourite 21st century movies into a different box and mailed it, in case they had not destroyed the DVD player and wanted something comforting to watch. The TARDIS hummed her approval and moved 200 years backwards instead of forwards in time, heading to a completely different galaxy than the Doctor had programmed into the coordinates.
So, that was a bit rubbish, yes. (ducks)