The Apostolic Princess of Rome-Ruthenia is the senior-most female office and title of the Pontifical Imperial State of Rome-Ruthenia and the United Roman-Ruthenian Church. It is held by the wife of the Pope of Rome-Ruthenia or, if unmarried, by a female relative he appoints. Her other titles include:

Princess of the Romans, Empress, and Archprincess of Rome-Ruthenia
Grand Duchess and titular Queen of Ruthenia and titular Tsaritsa of All Rus' (Old Russian State)
Duchess and Princess of Florence, Imperial Lady of Italy, Naples, Walsingham, and the Floridas
Princess and Electress of Würzburg, Princess and titular Queen of Etruria in the Holy Roman Empire
Duchess of Franconia and Archduchess of Zagros
Grand Princess of Kiev, Princess of Galicia-Volhynia, Vladimir, Novgorod, Peremyshl, Belz, Zvenygorod, and Terebovlia
Princess, Duchess, and Marquise of Santa Croce, Princess, Duchess, Marquise, and Countess of Monte Titano, Princess McIan of McShane
Countess of Sainte Animie, Valais, Daniell, Santa Croce, Vanzy, Johnson, Sommerhausen, Hausen bei Würzburg, Theilheim, and Estenfeld
Baroness of Saint Martin and Johnson, Lady des Loges, and others.

Further information

Pontifical and Imperial Household of Rome-Ruthenia · Pontifical and Imperial Highness