Mary was the eldest surviving child of James II (second son of Charles I) and his first wife, Anne Hyde; William was the only child of William II, Prince of Orange (who died of smallpox, eleven days before he was born), and his wife Mary, who was James's elder sister. William and Mary were married (much to her distress, apparently) in 1677, on his 27th birthday; she was just 15.
© Haydn Thompson 2017