CLASSIC!

A woman has twins, and gives them up for adoption. One of them goes to a family in Egypt and is named "Amal." The other goes to a family in Spain, they name him "Juan". Years later, Juan sends a picture of himself to his mum. Upon receiving the picture, she tells her husband that she wished she also had a picture of Amal. Her husband responds, "But they are twins. If you've seen Juan, you've seen Amal."