v 25. So King Solomon ordered Benaiah son of Jehoiada to execute him, and Adonijah was put to death.
Once on the throne, Solomon sets about eliminating rivals, including Adonijah one of his older brothers.
After the death of his elder brothers Amnon and Absalom, Adonijah considered himself the heir-apparent to the throne. He acquired chariots and a large entourage. Although the king was aware of this, he neither rebuked his son nor made any inquiry into his actions. David’s silence may have been interpreted by Adonijah and others as consent. Adonijah consulted and obtained the support of both the commander of the army Joab and the influential priest Abiathar. However, the priest Zadok; Benaiah, head of the king’s bodyguard; Nathan, the court prophet; and others did not side with Adonijah.
In anticipation of his father’s imminent death, Adonijah invited his brothers and the court officials to a solemn sacrifice in order to announce his claim to the throne. However, Adonijah was supplanted by Solomon through the influence of Bathsheba, and through the diplomacy of the prophet Nathan. They induced David to give orders that Solomon should immediately be proclaimed and admitted to the throne.
Adonijah fled and took refuge at the altar, receiving pardon for his conduct from Solomon on the condition that he showed himself a worthy man (1 Kings 1:5-53). He afterwards made a second attempt to gain the throne, by trying to marry Abishag from Shunem (You can read Abishag’s role in 1 Kings 1:1-4, which might explain Solomon’s reaction.), but Solomon denied authorization for such an engagement, even though Bathsheba now pleaded on Adonijah’s behalf. He was then put to death (1 Kings 2:13-25).