Adelheid Emma Wilhelmina Theresia (Arolsen, 2 August 1858 – Den Haag, 20 March 1934), Princess of Orange-Nassau, Princess of Waldeck-Pyrmont, was the second wife of king William III of the Netherlands. She was married to him from 1879 until he died in 1890. After his death, she became Queen-Regent of the Netherlands because her daughter Wilhelmina was only 10 when her father died, and too young to reign.