William IV, Grand Duke of Luxembourg

William IV
Grand Duke of Luxembourg
Reign	17 November 1905 – 25 February 1912
Predecessor	Adolphe
Successor	Marie-Adélaïde
Regent	Grand Duchess Maria Anna (1908–1912)
Prime Minister	Paul Eyschen
Born	(1852-04-22)22 April 1852 Biebrich Palace, Wiesbaden, Duchy of Nassau
Died	25 February 1912(1912-02-25) (aged 59) Berg Castle, Colmar-Berg, Luxembourg
Burial	Schlosskirche ("Castle Church") in Weilburg since 1953
Spouse	Infanta Marie Anne of Portugal (m. 1893)
Issue	Marie-Adélaïde, Grand Duchess of Luxembourg Charlotte, Grand Duchess of Luxembourg Hilda, Princess of Schwarzenberg Antonia, Crown Princess of Bavaria Elisabeth, Princess Ludwig Philipp of Thurn and Taxis Sophie, Princess Ernst Heinrich of Saxony
House	Nassau-Weilburg
Father	Adolphe, Grand Duke of Luxembourg
Mother	Princess Adelheid-Marie of Anhalt-Dessau
Religion	Protestantism

William IV (French: Guillaume Alexandre; 22 April 1852 – 25 February 1912) was Grand Duke of Luxembourg from 17 November 1905 until his death in 1912. He succeeded his father, Adolphe. Like his father, William mostly stayed out of politics despite being vested with considerable power on paper by the Constitution.

William was a Protestant, the religion of the House of Nassau. He married Infanta Marie Anne of Portugal, believing that a Roman Catholic country ought to have a Roman Catholic monarch. Thus his heirs have been Catholic.

At the death of his uncle, Prince Nikolaus-Wilhelm in 1905, the only other legitimate male in the House of Nassau-Weilburg was William's cousin, Georg Nikolaus, Count of Merenberg, the product of a morganatic marriage. So in 1907, William declared the Counts of Merenberg non-dynastic, naming his own eldest daughter Marie-Adélaïde (1894–1924) as heiress presumptive to the grand ducal throne. She became Luxembourg's first reigning grand duchess upon her father's death in 1912, and upon her own abdication in 1919, was succeeded by her younger sister Charlotte (1896–1985). Charlotte's descendants reign until the present day.

To date, William is the last monarch of Luxembourg to die on the throne.