Lady Anne Hyde (March 1637 – March 31, 1671), daughter of Edward Hyde, 1st Earl of Clarendon, became the first wife of James, Duke of York (the future King James II of England and VII of Scotland), and the mother of two queens, Mary II of England and Anne of Great Britain.
She was born, on either March 12 or March 22, 1637, at Windsor, Berkshire, to Frances (daughter of Sir Thomas Aylesbury, Master of Requests) and to Sir Edward Hyde (later -- from 1661 -- 1st Earl of Clarendon) of the Hyde of Norbury family. In 1659, at Breda in the Netherlands, she allegedly married James, then Duke of York, in a secret ceremony. The royal family at this time remained in exile following the English Civil War, and Anne's father served as the loyal Royalist chief adviser to the prospective King Charles II of England, James's elder brother.
The couple went through an official marriage ceremony on September 3, 1660, in London, following the Restoration of the monarchy. Their first child, Charles, was born less than two months later, but died in infancy, as did five further sons and daughters. Only two daughters survived: Mary (born 30 April 1662) and Anne (born 6 February 1665). A few weeks after the birth of their youngest child, Anne died of cancer at St. James's Palace and was buried in Westminster Abbey. According to the Dictionary of National Biography, she gave birth to "her eighth child, a daughter, on 9 February 1671, but by now her fatal illness, probably breast cancer, was in an advanced stage." 
Late in her life, the Duchess of York secretly converted to Catholicism, much to the horror of her staunchly Anglican family. After her death her widower also converted to the Roman Catholic faith (circa 1672). At the order of James's older brother King Charles, however, James and Anne's daughters received a Protestant education.
King James suffered deposition in a revolution against his Catholic rule in 1688, and Anne Hyde's daughter Mary and her son-in-law, William of Orange, jointly assumed the throne. After James, no British King or Queen has affirmed belief in the Catholic faith.