William III and Mary II co-reigned from 1689 to 1694. After Mary's death William ruled alone till 1702.
They were first cousins, Mary a daughter of their predecessor James II, and William a son of James' sister Mary who was married to the Prince of Orange.
So William, of the House of Orange-Nassau, came in from the Netherlands.
I have a Dutch coin commemorating the 300th anniversary of their ascension,
