A couple had been married for many years, and their son was old enough to date. One day, the son brought a girl home for dinner. The mother was thrilled with his choice and eagerly anticipated the wedding. However, the father seemed upset. Eventually, the son asked, "Dad, why aren't you happy with her? Mom likes her a lot."
The father explained, "Son, there's nothing wrong with the girl. It's just that I cheated on your mother long ago, and the girl you're dating is my daughter from that affair."
So, the son dumped her and found another girlfriend. Again, he brought her home, much to his mother's delight. But once more, the father told him this girl was also his half-sister. The son lost his temper and told his mother what his father had said.
Furious, the mother shouted, "Don't listen to him, sweetheart! He isn't even your father!"