Mother-Son story where the mother dies

[Clear_Nectarine_9244]

I only had read a few bits of the story but the story was that the son was making love to his wife for the last time as she had some illness. She died after that. I think they had 2/3 kids together. It was a plot twist near the end where the kids tell their father that they are aware that their mother is also their father's mother.