2 Samuel 13:2, 4

Amnon became so obsessed with Tamar that he became ill. She was a virgin, and Amnon thought he could never have her.

One day Jonadab said to Amnon, “What’s the trouble? Why should the son of a king look so dejected morning after morning?” So Amnon told him, “I am in love with Tamar, my brother Absalom’s sister.”