Aulic titulature
Aulic titulature is a term, derived from the Greek aulè and Latin aula (in the meaning palace) for hierarchic systems of titles specifically in use for court protocol.
Hellenistic Antiquity
Ironically in the formal "court" titulature of the Hellenistic empires ruled by dynasties we know as Diadochs, the title diadochos was not customary for the Monarch, but has actually been proven to be the lowest in a system of official rank titles, known as Aulic titulature, conferred - ex officio or nominatim - to actual courtiers and as an honorary rank (for protocol) to various military and civilian officials.
Notably in Lagid Egypt, diadochos was reported as the lowest aulic rank, under Philos (Basilikos) "Friend" (of the King), Archisomatophylax ("Arch-bodyguard"), protos philos ("First friend"), homotimos ("[nearly] equal dignitary") and syggeneus ("cognate of the crown"), during the reign of Ptolemaios V Epiphanes. A similar system of titles was in place in other Hellenistic monarchies.