The titles of "Christ" and "king" are not used together in the gospel, but "Christ" is in itself a royal title (i.e.
Outside of the gospel, the First Epistle to Timothy (6:14-15) explicitly applies the phrase of "king of kings and lord of lords" (Βασιλεὺς βασιλέων καὶ κύριος κυρίων), taken from the Pentateuch (Deuteronomy 10:17) to Jesus Christ.