One Sunday morning George burst into the living room and said, "Dad! 
Mom! I have some great news for you! I am getting married to the most 
beautiful girl in town. She lives a block away and her name is Susan. 
After dinner, George's dad took him aside, "Son, I have to talk with 
you. Look at your mother, George. She and I have been married 30 
years, she's wonderful wife and mother, but she has never offered much 
excitement in the bedroom, so I used to fool around with women a lot. 
Susan is actually your half sister, and I'm afraid you can't marry her." 

George was broken-hearted. After eight months he eventually started 
dating girls again. A year later he came home and very proudly 
announced, "Dianne said yes! We're getting married in June." 

Again his father insisted on another private conversation and broke the 
sad news. "Dianne is your half sister too, George. I awfully sorry 
about this." 

George was livid! He finally decided to go to his mother with the news 
his father had shared. "Dad has done so much harm. I guess I'm never 
going to get married," he complained. "Every time I fall in love, Dad 
tells me the girl is my half sister." "Heh, heh," his motherchuckled, 
shaking her head, "don't pay any attention to what he says. He's not 
really your father....."