2 Samuel 13:27

But Absalom pressed him, that he let Amnon and all the king’s sons go with him.

Absalom pressed David until he let Amnon and all the king's sons go with him to Absalom's feast for the king's sons. He had concealed his purpose of revenge for two full years in order to strike more surely as the natural protector of his foully wronged sister. David, self-condemned by his own sin, had let the shameful crime of Amnon his first-born pass unpunished and unrebuked, though the law pronounced death upon the adulterer and Amnon's unnatural crime made him doubly guilty.

At that feast the drunken, incestuous Amnon was slain by his brother's command as Absalom avenged Amnon's crime. The slaying was twofold judgment meted out to David under his own fourfold sentence that four of his sons must fall for his sin. The killing brought home to David the bitter fruits of his own wrongdoing and continually reminded him of the injustice he had done to Uriah and Bath-sheba.