On 20 April 1663, the twelve-year-old Anne married the fourteen-year-old James Crofts, 1st Duke of Monmouth, the oldest illegitimate son of Charles II (eldest surviving son of Charles I), by his mistress, Lucy Walter. James had been born in Rotterdam during the Second English Civil War, where his father was with his sister, Mary and his brother-in-law William II, Prince of Orange. The couple had six children: