Hello, In my novel a boy and his sister have sex by mistake, not knowing each other's identities, and realise who they are the morning after. They then live (and were living) separately for five years, and then meet again. Unbeknownst to the (now) man, his sister gave birth to the child, who was then kidnapped by her aunt and renamed so that she never finds her son again. I can't portray a realistic aftermath for both characters after these events. When he's having sex with his wife, images of his sister keep popping back up so he eventually marries his sister off to 'get rid' of her. This is all set in the 5th century in Britain.