Amnon violated his sister Tamar
But Absalom did not speak to Amnon either good or bad; for Absalom hated Amnon because he had violated his sister Tamar. Now it came about after TWO FULL YEARS that Absalom had sheepshearers in Baal-hazor, which is near Ephraim, and Absalom invited all the king’s sons. (2SA 13:22-23)