Last child

Once a husband and wife lived in a old town, they had four kids the first three were slim and had brown hair, the last one was fat and had black hair.

Husband-Darling, I am going to die (he had cancer). Please do tell me is our last child really ours.

Wife-I swear you, he is really ours.
Hearing this the husband died peacefully.

Wife-Thank god, "He didn't ask about the first three..."