Complex sentence: His/Her Grand Ducal Highness (acronym: HGDH) is a style of address used before the princely titles of the non-reigning members of some German ruling families headed by a Grand Duke.
Split into simpler sentences: His/Her Grand Ducal Highness (acronym HGDH). The style of HGDH appeared at the front of the princely titles of the non-reigning members of some German ruling families headed by a Grand Duke.