William IV was Grand Duke of Luxembourg for a handful of years in the early 20th Century.

He was born on April 22, 1852, at Biebrich Palace, in Wiesbaden, in the Duchy of Nassau. His father was Adolphe, then Duke of Nassau and later Grand Duke of Luxembourg; and his mother was Princess Adelheid-Marie of Anhalt-Dessau. William was their oldest child and so was the heir apparent to the title of Duke of Nassau.

Luxembourg had, since 1815, been an independent entity of sorts; actually, it was in personal union with the Netherlands, under the rule first of William I and then of his also-named descendants, William II and William III. When that monarch was seriously ill near the end of his reign, Adolphe served as regent in Luxembourg. Thus, he was well placed to assume the title of Grand Duke of Luxembourg in 1890, when William III died.

The duke-in-waiting, William IV, married Infanta Marie Anne of Portugal (daughter of King Miguel I) on June 21, 1893, in Fischhorn Castle, in Zell am See. The couple had six children: Marie-Adélaide (1894), Charlotte (1896), Hilda (1897), Antonia (1899), Elisabeth (1901), and Sophie (1902).

Adolphe died on Nov. 17, 1905, and William assumed the title of Grand Duke of Luxembourg. Because he had no son, he declared his oldest daughter his successor. When he died, on Feb. 25, 1912, at Berg Castle in Colmar-Berg, she did indeed succeed him, becoming the first Grand Duchess of Luxembourg.