As such, their children currently use the styles HI&RH as members of both the royal family of Belgium and the Imperial House of Habsburg-Lorraine.
It may be used for the head of the House of Hohenzollern out of respect; however, like all members of former German noble families, in law he is considered to be an ordinary citizen of Germany, and as such holds no title officially.
One contemporary example of this is HI&RH Lorenz, Archduke of Austria-Este, Prince of Belgium, 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.
Grand Duchess Elena Vladimirovna of Russia, upon her marriage to Prince Nicholas of Greece, was styled Her Imperial and Royal Highness.