William called William of Winchester, William Longsword, or William of Lüneburg, was the youngest son of Duke Henry the Lion

Henry the Lion

Henry the Lion was a member of the Welf dynasty and Duke of Saxony, as Henry III, from 1142, and Duke of Bavaria, as Henry XII, from 1156, which duchies he held until 1180....

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William was born in England during his father's exile; he remained there when Henry returned to Saxony

Duchy of Saxony

The medieval Duchy of Saxony was a late Early Middle Ages "Carolingian stem duchy" covering the greater part of Northern Germany. It covered the area of the modern German states of Bremen, Hamburg, Lower Saxony, North Rhine-Westphalia, and Saxony-Anhalt and most of Schleswig-Holstein...

 and was raised at Richard Lionheart's court. When Henry died in 1195, William inherited Henry's properties around Lüneburg

Lüneburg

Lüneburg is a town in the German state of Lower Saxony. It is located about southeast of fellow Hanseatic city Hamburg. It is part of the Hamburg Metropolitan Region, and one of Hamburg's inner suburbs...

, near Lauenburg, and in the eastern Harz

Harz

The Harz is the highest mountain range in northern Germany and its rugged terrain extends across parts of Lower Saxony, Saxony-Anhalt and Thuringia. The name Harz derives from the Middle High German word Hardt or Hart , latinized as Hercynia. The legendary Brocken is the highest summit in the Harz...

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In 1202, William married Helena, daughter of King Valdemar I of Denmark

Valdemar I of Denmark

Valdemar I of Denmark , also known as Valdemar the Great, was King of Denmark from 1157 until 1182.-Biography:...

. Their only child was Otto (1204-1252), who inherited his father's property.

Ancestors