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 subtle man. And he said unto him, Why, O son of the king, art thou thus lean from day to day? wilt thou not tell me? And Amnon said unto him, I love Tamar, my brother Absalom’s sister.