2 Samuel 13:3-4

But Amnon had a friend whose name was Jonadab the son of Shimeah, David’s brother; and Jonadab was a very shrewd (cunning) man. He said to Amnon, “Why are you, the king’s son, so depressed morning after morning? Will you not tell me?” And Amnon said to him, “I am in love with Tamar, my [half-] brother Absalom’s sister.”