Marie-Adélaïde (, ; 14 June 1894 – 24 January 1924), was Grand Duchess of Luxembourg from 1912 until her abdication in 1919. She was the first Grand Duchess regnant of Luxembourg (after five grand dukes), its first female monarch since Duchess Maria Theresa (1740–1780, who was also an Austrian archduchess and Holy Roman Empress) and the first Luxembourgish monarch to be born within the territory since Count John the Blind (1296–1346).
Named as heiress presumptive by her father Grand Duke William IV in 1907 to prevent a succession crisis due to his lack of a son, Marie-Adélaïde became Grand Duchess aged 17 upon his death in 1912. She ruled through the First World War, and her perceived support for the German occupation forces led to great unpopularity in Luxembourg as well as neighbouring France and Belgium. On the advice of Parliament and under enormous pressure from the Luxembourgish people, she abdicated on 14 January 1919 in favour of her younger sister Charlotte, who managed to save the monarchy and the dynasty in a national referendum later that year.
Following her abdication, Marie-Adélaïde retired to a convent in Italy, before leaving due to ill health. She died of influenza in Germany on 24 January 1924, at the age of 29.
Early years
thumb|upright|Princess Marie-Adélaïde (1909)
Marie-Adélaïde was born on 14 June 1894 at Berg Castle, the eldest child of Grand Duke William IV and his wife, Infanta Marie Anne of Portugal.
Since her father had six daughters and no sons, he proclaimed Marie-Adélaïde as the heir presumptive on 10 July 1907, in order to solve any succession crisis due to the use of Salic law in the monarchy.
Due to that same Salic Law, the elder branch of the House of Nassau, called Nassau-Weilburg (present-day Luxembourg-Nassau) inherited in 1890 the throne of Luxembourg from the younger branch called Nassau-Orange, which was not only supplying the grand dukes of Luxembourg from 1815 to 1890, but was also in a personal union the reigning dynasty of the Kingdom of the Netherlands.
Thus, when her father died on 25 February 1912, she succeeded to the throne at the age of 17, becoming the first reigning Grand Duchess of Luxembourg. Her mother served as regent until Marie-Adélaïde's eighteenth birthday on 18 June 1912, when the President of the Chamber Auguste Laval swore her in as the first Luxembourgish monarch to be born in the territory since John the Blind (1296–1346)
. Laval's speech to the Chamber of Deputies (parliament) during the ceremony was: