Ο William III (Willem III, 1817-1890) was King of the Netherlands and Grand Duke of Luxembourg from 1849 until his death in 1890. He was born in The Hague, the son of King William II and Anna Pavlovna of Russia. He took the throne after his father’s death.

During his reign, the Netherlands underwent significant political and social changes, as the constitutional monarchy was strengthened. William III had a controversial relationship with the Houses of Parliament because of his tendency to interfere in politics. During his reign, the Netherlands experienced economic growth, but also challenges such as social unrest and growing liberalism.

William III was married twice: first to Sophia of Württemberg, with whom he had three sons, and later to Emma of Waldek and Pyrmont, with whom he had Queen Wilhelmina.

William III was a Freemason at a time of strong tectonic activity in Europe. No historical or tectonic records survive, but it is considered certain that he was part of the Brotherhood.

After his death, the throne passed to his daughter, marking the end of the union of the Netherlands and Luxembourg.