John William Friso, Prince of Orange

John William Friso, Prince of Orange-Nassau (Dutch: Johan Willem Friso van Oranje-Nassau; 14 August 1687 – 14 July 1711) became the titular Prince of Orange in 1702. He was stadtholder of Friesland until his death by drowning in the Hollands Diep in 1711. Along with his wife, Marie Louise, Friso is the ancestor of all European monarchs occupying the throne today.

He was the son of Henry Casimir II, Prince of Nassau-Dietz, and Princess Henriëtte Amalia of Anhalt-Dessau who were both first cousins of William III. As such, he was a member of the House of Nassau, and through the testamentary dispositions of William III became the progenitor of the new line of the House of Orange-Nassau.

With the death of William III, Prince of Orange, the legitimate male line of William the Silent (the second House of Orange) became extinct. John William Friso, the senior agnatic descendant of William the Silent's brother and a cognatic descendant of Frederick Henry, grandfather of William III, claimed the succession as stadtholder in all provinces held by William III. This was denied to him by the republican faction in the Netherlands.

The five provinces over which William III ruled – Holland, Zeeland, Utrecht, Gelderland and Overijssel – all suspended the office of Stadtholder after William III's death. The remaining two provinces – Friesland and Groningen – were never governed by William III, and continued to retain a separate Stadtholder, John William Friso. He established the third House of Orange, which became extinct in the male line in 1890. His son William IV, Prince of Orange, however, later became stadtholder of all seven provinces.

John William Friso's position as William III's heir general was opposed by King Frederick I of Prussia, who also claimed (and occupied) part of the inheritance (for example Lingen). Under William III's will, Friso stood to inherit the Principality of Orange. However, the Prussian King Frederick I also claimed the Principality of Orange in the Rhône Valley, of which he later ceded the territory to France.

On coming of age in 1707, John William Friso became a general of the Dutch troops during the War of Spanish Succession, under the command of the Duke of Marlborough, and turned out to be a competent officer. He commanded Dutch infantry in the battle of Oudenarde, siege of Lille, and battle of Malplaquet. The prestige that he acquired from his military service should have favored his eventual elevation as stadtholder in the remaining five provinces. However, in 1711, when traveling from the front in Flanders to meet the king of Prussia in The Hague in connection with his suit in the succession dispute, he drowned on 14 July when the ferry boat on the Moerdyk was overturned in heavy weather. His son was born six weeks after his death.

On 26 April 1709, he married Princess Maria Louise of Hesse-Kassel (1688–1765), daughter of Charles I, Landgrave of Hesse-Kassel, and granddaughter of Jacob Kettler, Duke of Courland. They had two children.

John William Friso and his wife are the most recent common ancestors to all currently reigning European monarchs. This is a title he has held since 1938, when Franz Joseph II -a descendant of John William Friso, succeeded Franz I - who was not a descendant, as Prince of Liechtenstein.