Alexander Joseph GCB (Bulgarian: Александър I Батенберг; 5 April 1857 – 23 October 1893), known as Alexander of Battenberg, was the first prince (knyaz) of modern Bulgaria from 1879 until his abdication in 1886.

Alexander was the second son of Prince Alexander of Hesse and by Rhine by the latter's morganatic marriage with Countess Julia von Hauke. The Countess and her descendants gained the title of Princess of Battenberg (derived from an old residence of the Grand Dukes of Hesse) and the style Durchlaucht ("Serene Highness") in 1858. Prince Alexander was a nephew of Russia's Tsar Alexander II, who had married a sister of Prince Alexander of Hesse; his mother, a daughter of Count Moritz von Hauke, had been lady-in-waiting to the Tsaritsa. Alexander was known to his family, and many later biographers, as "Sandro".

Alexander's brother, Prince Louis of Battenberg, married Princess Victoria of Hesse and the Rhine, a granddaughter of Queen Victoria. Their children included Queen Louise of Sweden, Earl Mountbatten of Burma and Princess Alice, the mother of Prince Philip, Duke of Edinburgh, husband of Queen Elizabeth II.

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