Apostolic King
Apostolic King was a hereditary title borne by the King of Hungary. Saint Stephen (ca. 997–1038) was supposed to have received it from Pope Sylvester II. The king's efforts to Christianize his people led to his comparison to one of the apostles. It was first used by the Holy Roman Emperor Leopold I (1657–1705) as King of Hungary. The title was last used in the reign of Charles IV (1916–18).
The title is comparable to Spain's Catholic and France's Most Christian King but is of a higher order.