Illustrious Highness
The Mountbatten family are a branch of the German house of Battenberg. The Battenberg family was a morganatic branch of the House of Hesse-Darmstadt, rulers of the Grand Duchy of Hesse in Germany. The first member of the House of Battenberg was Julia Hauke, whose brother-in-law Grand Duke Louis III of Hesse created her "Countess of Battenberg" with the style "Illustrious Highness" in 1851, on the occasion of her morganatic marriage to Grand Duke Louis' brother Prince Alexander of Hesse and by Rhine. Julia was elevated in her title to "Princess of Battenberg" with the style "Serene Highness" (HSH) in 1858.