Jamieson, Fausset and Brown on 2 Samuel 16:15-19

15-19. Hushai said unto Absalom, God save the king--Hushai's devotion to David was so well-known, that his presence in the camp of the conspirators excited great surprise. Professing, however, with great address, to consider it his duty to support the cause which the course of Providence and the national will had seemingly decreed should triumph, and urging his friendship for the father as a ground of confidence in his fidelity to the son, he persuaded Absalom of his sincerity, and was admitted among the councillors of the new king.

2Sa 16:20-23. Ahithophel's Counsel.