The ruler of Russia is called the tsar or emperor (the titles are interchangeable); his wife is either the tsaritsa or empress; and his male heir is called the tsarevich. His other children are given the titles of grand duke if male, or grand duchess if female.These last titles are passed down just one more generation, so a tsar’s grandchildren are also grand dukes and grand duchesses. But a tsar’s great grandchildren hold only the rank of prince or princess. Thus grand dukes and grand duchesses outrank princes and princesses.
From Before You Begin in The Family Romanov: Murder, Rebellion, and the Fall of Imperial Russia.
Photo: The family of Tsar Nicholas II of Russia. Left to right: Grand Duchess Olga, Grand Duchess Maria, Nicholas II, Alexandra, Grand Duchess Anastasia, Tsarevich Alexei, Grand Duchess Tatiana.
Photo Attribution: By Boissannas et Eggler, St. Petersburg, Nevsky 24. [Public domain], via Wikimedia Commons