2 Samuel 13:2, 4

Amnon was so frustrated because of his [half-] sister Tamar that he made himself sick, for she was a virgin, and Amnon thought it impossible for him to do anything to her.

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.”