HGDH is an acronym for His Grand Ducal Highness or Her Grand Ducal Highness. The style of HGDH appeared at the front of the princely titles of the non-reigning members of German ruling families headed by a Grand Duke. No current reigning family employs the style. It was, however, used by the younger sisters of the late Grand Duchess Charlotte of Luxembourg. Since Grand Duchess Charlotte's marriage to Prince Felix of Bourbon-Parma, all of their descendants have used the style Royal Highness.

A reigning Grand Duke, his heir apparent, and their spouses, would use the title Royal Highness. The male line descendants of a reigning Grand Duke, other than the heir, would use the title Grand Ducal Highness. This practice was followed by the ruling families of Luxembourg, Hesse, Baden, Saxe-Weimar, Mecklenburg-Schwerin, Mecklenburg-Strelitz and Oldenburg. Other Grand Ducal families either existed before this system developed or were controlled by different rules.

Russian Grand Dukes/Grand Duchesses were the children or grandchildren of the Emperor and used the style Imperial Highness. The Grand Dukes of Tuscany used the style Royal Highness for themselves but it is not clear what title other members of the family would have used. By the time the system of different classes of Highness came into regular use for the relatives of rulers (in the nineteenth century), the Grand Dukes of Tuscany were also members of the House of Austria. As such, they had the title of Archduke and used the style Imperial and Royal Highness.

In most of Europe, the style of Grand Ducal Highness was considered to be lower in rank than Royal Highness, and Imperial Highness, but higher in rank that Serene Highness, and Highness. If a woman with the rank of Royal Highness married a man with the rank Grand Ducal Highness, the woman would usually retain her pre-marital style.

External Links

• Article on the use of the style Highness