The title “King” (Βασιλεύς) is used in the Greek Liturgies and Fathers of the Roman Emperor, as in the Clementine Liturgy:  ὑπὲρ τοῦ βασιλέως, καὶ τῶν ἐν ὑπεροχῇ, where it is taken from 1 Tim. ii. 2.  Compare Cat. xiv. 14, and 22:  Κωνσταντίνου τοῦ βασιλέως.