Illustrious Highness

His/Her Illustrious Highness (abbreviation: H.Ill.H.) is the English-language form for a style used by certain members of the European .

It is used to translate the Middle High German word Erlaucht (German: erleuchtet), similar to the later Durchlaucht which was reserved for the Reichsfürsten (Princes of the Holy Roman Empire).

From the Early modern period, the style Erlaucht has been used by the members of those comital families (Reichsgrafen) who, like the Reichsfürsten, held the status of Imperial immediacy. They retained it even after the German Mediatisation of 1802/03, confirmed by the Bundesversammlung of the German Confederation in 1828.

The style was also adopted by the cadet members of some princely families like Colloredo-Mansfeld, Fugger, Khevenhüller, Salm, Schönburg, Starhemberg, Stolberg, Waldburg or Waldeck-Pyrmont. Mediate comital families were entitled to the style Hochgeboren.

It is sometimes used to translate the Russian word Ssiatelstvo (Сиятельство), a style used by members of some Russian princely families (also sometimes translated as Serene Highness).

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