"William VI (4 July 1535 – 20 August 1592), called William the Younger (German: Wilhelm der Jüngere), was Duke of Brunswick-Lüneburg and Prince of Lüneburg from 1559 until his death. Until 1569 he ruled together with his brother, Henry of Dannenberg.
William was the son of Ernest I, Duke of Brunswick-Lüneburg. On 12 October 1561 he married Dorothea of Denmark (29 June 1546 Kolding–6 January 1617 Winsen), daughter of Christian III of Denmark and Dorothea of Saxe-Lauenburg.
In 1582, William began suffering from fits of insanity. These fits caused his wife to flee him in 1584 for her own safety." - (en.wikipedia.org 17.10.2020)