A husband and wife have four boys.
The odd part of it is that the older three have red hair, light skin, and are tall, while the youngest son has black hair, dark eyes, and is short.
The father eventually takes ill and is lying on his deathbed when he turns to his wife and says,
“Honey, before I die, be completely honest with me. Is our youngest son my child?”
The wife replies, “I swear on everything that’s holy that he is your son.”
With that, the husband passes away.
The wife then mutters, “Thank God he didn’t ask about the other three.”