I watched a documentary a while ago about cases like that. Where although they knew they were blood related they had little contact as youngsters and sexual relationships started. There was a father and daughter who had a daughter together too. The way the show was I actually kinda felt sorry for them. They didn't want to be in love. But at the same time adults should have some self restraint. This is a case more of a 32 year old taking advantage of a child really.