Princess Marie of Saxe-Altenburg (Marie Friederike Leopoldine Georgine Auguste Alexandra Elisabeth Therese Josephine Helene Sophie; 2 August 1854 – 8 October 1898) was the wife of Prince Albert of Prussia, Regent for the duchy of Brunswick.

Marie was the only surviving child of Ernst I, Duke of Saxe-Altenburg and his wife Princess Agnes of Anhalt-Dessau, as her younger brother Georg died as an infant. Because her father had no surviving sons to inherit his title, he was succeeded by Marie's cousin Ernst.

Marie arrived at Potsdam on the evening of 18 April 1873, where she was received by Prince Albert of Prussia, her fiance. The couple drove to Bellevue Castle, where they were received by the Emperor and Empress.

On 9 April 1873 in Berlin, Marie married Prince Albert, a grandson of Frederick William III of Prussia. Other reports have them being married on 19 April. Albert's parents had been unhappily married to each other and later divorced; as he chose to wait before getting married and was 36 at the time of their wedding, this is believed to be the reason he did not marry earlier. Spectators commented that the wedding ceremony was grander than most, with Dragoon Guards opening the procession and the Emperor and Empress in attendance. Marie was described as possessing "girlish beauty, and [a] modest unpretending demeanor" that "at once captivated the hearts of the multitude".

They had the following children:

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