Habsburg Use
The style is used by members of the Habsburg dynasty, who use the titles Prince Imperial and Archduke of Austria and Prince Royal of Bohemia and Hungary. One contemporary example of this is HI&RH Prince Lorenz, Archduke of Austria-Este, who is a member of the Imperial House of Habsburg-Lorraine by birth and of the Belgian Royal Family by marriage. The Habsburgs, who have held the elective Crown of the Holy Roman Empire for centuries, only began to use the style Imperial and Royal Highness with the establishment of the hereditary Austrian Empire in 1804; prior to this, non-reigning members of the dynasty were styled as Royal Highnesses.
Read more about this topic: Imperial And Royal Highness