“She wanted to tell me. Maybe she even tried. But she couldn't. It wasn't because I was only twelve. It was because I was her child, created by her and Father because they wanted to be in bed together and nothing else would do, nobody else would do. You see? … Because to the child, he was not created by his mother's and his father's passion or capacity for it. He couldn't have been because he was there first, he came first, before the passion; he created the passion, not only it but the man and the woman who served it; his father is not his father but his son-in-law, his mother not his mother but his daughter-in-law if he is a girl. … and if a boy or a girl really is his father's and her mother's father-in-law or mother-in-law, which would make the girl her brother's mother no matter how much younger she was, then a girl with just one brother and him a twin at that, would maybe be his wife and mother too.”

Charles Mallinson in Ch. 19; Charles Mallinson's mother, Maggie, and his uncle, Gavin Stevens, besides being their parents' only children, are twins.
The Town (1957)