2 Samuel 8:15-18

David's officers

15 David ruled over all Israel. He did everything that was right and fair for all his people. 16 Zeruiah's son, Joab, was the leader of Israel's army. Ahilud's son, Jehoshaphat, wrote down the important things that happened. 17 Ahitub's son Zadok and Abiathar's son Ahimelech were priests. Seraiah was David's secretary. 18 Jehoiada's son Benaiah was the leader of David's personal guards. David's sons served as priests.

8:18David's personal guards (bodyguards) were men who belonged to the Kerithite and Pelethite people.
8:18David belonged to Judah's tribe, so his family could not be priests. Only Aaron's descendants could be priests. They belonged to Levi's tribe. Perhaps ‘priest’ here means that they helped David in a special way.