So, when he furnished them with their provisions, he said, "Bring me a step- brother of yours who is from your father. Do you not see that I give full measure of grain and that I am the best of hosts?"
Translation endnotes
[12:59] Joseph was hiding his identity from his brothers. Wouldn't his knowledge about their missing brother give him away? Perhaps, Joseph prepared them for this by letting them talk about their family before; or, it was known by his brothers that he had official records about their family.