2 Samuel 13:38

And it came to pass after this, that Absalom the son of David had a fair sister, whose name was Tamar; and Amnon the son of David loved her.

And Amnon was so vexed, that he fell sick for his sister Tamar; for she was a virgin; and Amnon thought it hard for him to do any thing to her.

But Amnon had a friend, whose name was Jonadab, the son of Shimeah David's brother: and Jonadab was a very subtil man.

And he said unto him, Why art thou, being the king's son, lean from day to day? wilt thou not tell me? And Amnon said unto him, I love Tamar, my brother Absalom's sister.