Io is a particle of a title used mainly by Romanian royalty from both Moldavia and Walachia, preceding their names and the complete list of titles, in all their documents (written or engraved), since the formation of the respective principalities up to the Hohenzollern dynasty in the 19th century.
First used by the Assenid kings, the particle is the abbreviation of name Ioan (English: John, Latin: Ioannes), which comes from the original Hebrew Yohanan, meaning "God has favoured". Thus, in this context, the particle has the meaning "By the grace of God" (see divine right), rather than alluding to an actual name of John. It was always spelled with a Latin I and a Greek omega (in both Latin and Cyrillic documents). In some Latin accounts it was replaced by "Iohannes".