2 Samuel 13:1-4

ABSALOM SON of David had a fair sister whose name was Tamar, and Amnon [her half brother] son of David loved her. And Amnon was so troubled that he fell sick for his [half] sister Tamar, for she was a virgin, and Amnon thought it impossible for him to do anything to her. But Amnon had a friend whose name was Jonadab son of Shimeah, David's brother; and Jonadab was a very crafty man. He said to Amnon, Why are you, the king's son, so lean and weak-looking from day to day? Will you not tell me? And Amnon said to him, I love Tamar, my [half] brother Absalom's sister.