Princess Louise of Saxe-Gotha-Altenburg (Louise Dorothea Pauline Charlotte Fredericka Auguste; 21 December 1800 – 30 August 1831) was the wife of Ernst I, Duke of Saxe-Coburg and Gotha and the mother of Duke Ernst II and Prince Albert, husband of Queen Victoria. She is also the paternal great-great-great grandmother of Elizabeth II.

Princess Louise was the only daughter of Augustus, Duke of Saxe-Gotha-Altenburg and his first wife Louise Charlotte of Mecklenburg-Schwerin, daughter of Frederick Francis I, Grand Duke of Mecklenburg-Schwerin and Princess Louise of Saxe-Gotha-Altenburg (her namesake).

On 31 July 1817 in Gotha, sixteen-year-old Louise married her thirty-three-year-old kinsman Ernst III, Duke of Saxe-Coburg-Saalfeld after he failed to win the hand of a Russian grand duchess. Louise was considered "young, clever, and beautiful".

They had two children: Ernst, who inherited his father's lands and titles, and Albert, who was later the husband of Queen Victoria.

The marriage was unhappy because of Ernst's infidelities and the couple separated in 1824. St. Wendel, in the Principality of Lichtenberg, was assigned as her new residence (it was an exclave of Saxe-Coburg und Gotha; see Sotnick on this period), and Louise was forced to leave her two sons behind. Biographer Lytton Strachey noted in 1921: "The ducal court was not noted for the strictness of its morals; the Duke was a man of gallantry, and it was rumored that the Duchess followed her husband's example. There were scandals: one of the Court Chamberlains, a charming and cultivated man of Jewish extraction, was talked of; at last there was a separation, followed by a divorce."

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