Quote Originally Posted by DEfiat View Post
I know a guy whose teenage boy was showing interest in a certain teenage girl. The father objected and discouraged a relationship. The son persisted and saw no reason he shouldn't date the girl. Finally the father shared his big secret with his son: he had fathered some children out of wedlock and the girl was his half-sister.
Many a time has this happened. A half sister and half brother are highly attracted to each other and don't even know why--get married, etc.