Who married George William, Duke of Brunswick-Lüneburg?

George William (German: Georg Wilhelm; 26 January 1624 – 28 August 1705) was the first Welf Duke of Lauenburg after its occupation in 1689. From 1648 to 1665, he was the ruler of the Principality of Calenberg as an appanage from his eldest brother, Christian Louis, Prince of Luneburg. When he inherited Luneburg on the latter's death in 1665, he gave Calenberg to his younger brother, John Frederick.

Nevertheless, he only kept the sub-division of Celle, giving the rest of Luneburg to their youngest brother Ernest Augustus, whose son, George Ludwig (future King of Great Britain), inherited Saxe-Lauenburg and Celle from George William. His only daughter, Sophia Dorothea of Celle, was George Ludwig's wife.

Éléonore Desmier d'Olbreuse (3, 7 or 9 January 1639 – 5 February 1722), was a French noblewoman, who became first the mistress and later wife of George William of Brunswick, Duke of Lauenburg and Prince of Celle. She was the mother of Sophia Dorothea of Celle, who was the wife of George I of Great Britain. Thus she was the maternal grandmother of George II.