Sancho VI William (Basque: Antso Gilen, French: Sanche Guillaume, Gascon: Sans Guilhem, Spanish: Sancho Guillén) (died 4 October 1032) was the Duke of Gascony from 1009 to his death. His reign is most notable for the renewal of Gascons ties with Spain.
In 1027, he met William V at Blaye and they jointly selected Geoffrey, a Frank, as Archbishop of Bordeaux, which had become the Gascon capital during Sancho's reign. He had given his sister Brisca in marriage to the widower duke William and when he died without successors in 1032, the Aquitainian duke's children by this second marriage inherited Gascony.
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