Ron knew, of course. He wasn't stupid, just not school-smart. This was not the kind of thing they prepared you for at Hogwarts.
He hadn't missed the owls while his wife thought he was asleep. The times she came home just a little too late from work and her excuse was delivered with just slightly flushed cheeks. Hermione had never been a good liar.
And he really knew when she got pregnant. Every time that they had had sex, Ron had been sure to use a contraception charm. When he had mentioned this to Harry, the emerald-eyed man had simply shrugged and told him that in the heat of the moment he must have slipped up on the pronunciation. 'You know how fiddly these spells are' he'd said.
Ron didn't ask Hermione, because he knew his wife would never be able to lie to him about something this big and Ron loved Hermione whatever she did. He didn't want to lose her.
He couldn't bring himself to wish the baby any harm. Being pregnant made Hermione happy, and that was all he could ever ask for. Besides, Ron would never, could never, wish a miscarriage on any woman, or any unborn baby, for that matter.
When Rose was born, Ron was the first to hold her after the midwife, while Hermione was still resting. It wasn't that she had tufts of her mother's brown hair rather than the Weasley red. It wasn't her slightly pointed chin, or her pale skin - it was those eyes, like the sky during a thunderstorm; liquid mercury.
But as soon as he held the tiny, fragile baby in his arms he knew that he loved her anyway. Ron loved the little girl more than anything else in the world, apart from his wife, and it didn't matter even one tiny bit if she was not his flesh and blood.
The owls stopped soon after Hermione announced that she was pregnant, and from the way she suddenly turned to him one day and announced, with a force that the proclamation had not held for a couple of years, "I love you, Ronald, I really do", he knew that she was no longer meeting with him.
Ronald Weasley watched his daughter grow up with pride. He taught her to fly and play quidditch. He watched her gobble up books, just like her mother. He saw her pick up his habits, subtle pieces of body language like rubbing the bridge of her nose when she was nervous. And he never once saw her smirk.
His little girl was always getting into trouble, and often beat Albus Potter in her adventures - she was fearless and ruthless in her protection of her friends and family (resulting in a few broken lips at the muggle primary school Hermione insisted that she attend), and it was no surprise when she was sorted into Gryffindor.
Just like her mother and just like Ron.
He only considered bringing up the subject once, on Rose's seventeenth birthday. He thought that perhaps she would want to know - she certainly had the right to. But he didn't want to upset Hermione by revealing that he knew, and so Rose remained ignorant of that one, insignificant fact (probably the only thing, he chuckled to himself, that his little bookworm didn't know).
Ultimately, you see, Ron had won. He got to see Rose's first smile, first steps, first word, first day at school, first crush, and so many more after that. He got to watch her face on Christmas morning as she unwrapped her presents (and yet another jumper from Grandma Weasley) and he got to walk her up the aisle. Ron got Hermione and Rose.
Once and for all, he beat Draco Malfoy.
A/N: Family is a feeling, not a biological term.
I just thought it had to be said - there are all these fics where Rose is actually Draco's and it's all revealed when she's sorted into Slytherin and suddenly Hermione and Draco move in together and they're all one happy family, leaving Ron behind.
In these fics it always seems that Rose has her father's smirk and sometimes she never even bonded with Ron - that's just not how it works. People pick up things like smirks from the people they see every day, they're not born with them. The people you live with influence you more, personality-wise, than DNA ever could.
I hope you liked it, even though it was short, and please review on your way out and check out the poll on my profile if you have time :D