Hungary
Before 1947, the style His/Her Serene Highness (Ő Főméltósága, literally: "His/Her High Dignity") was in use in Hungary. Princes were entitled to use it, and between 1920 and 1944 the regent, Miklós Horthy, was styled as His Serene Highness the Regent of the Kingdom of Hungary (Ő Főméltósága a Magyar Királyság Kormányzója).
Read more about this topic: Serene Highness