The Fourth Child...

A man lies on his deathbed, surrounded by his family: a weeping wife and four children. Three of the children are tall, good-looking and athletic; but the fourth and youngest is an ugly runt.
"Darling wife," the husband whispers, "assure me that the youngest child really is mine. I want to know the truth before I die, I will forgive you if..."
The wife gently interrupts him. "Yes, my dearest, absolutely, no question, I swear on my mother's grave that you are his father."
The man then dies, happy.
The wife mutters under her breath: "Thank God he didn't ask about the other three."