Jamieson, Fausset and Brown on Jeremiah 22:18

18. Ah my brother! ... sister!--addressing him with such titles of affection as one would address to a deceased friend beloved as a brother or sister (compare 1Ki 13:30). This expresses, They shall not lament him with the lamentation of private individuals [Vatablus], or of blood relatives [Grotius]: as "Ah! lord," expresses public lamentation in the case of a king [Vatablus], or that of subjects [Grotius]. Henderson thinks, "Ah! sister," refers to Jehoiakim's queen, who, though taken to Babylon and not left unburied on the way, as Jehoiakim, yet was not honored at her death with royal lamentations, such as would have been poured forth over her at Jerusalem. He notices the beauty of Jeremiah's manner in his prophecy against Jehoiakim. In Jr 22:13, 14 he describes him in general terms; then, in Jr 22:15-17, he directly addresses him without naming him; at last, in Jr 22:18, he names him, but in the third person, to imply that God puts him to a distance from Him. The boldness of the Hebrew prophets proves their divine mission; were it not so, their reproofs to the Hebrew kings, who held the throne by divine authority, would have been treason.

Ah his glory!--"Alas! his majesty."