Marlborough House, a Grade I listed mansion in St James's, City of Westminster, London, is the headquarters of the Commonwealth of Nations and the seat of the Commonwealth Secretariat. It was built in 1711 for Sarah Churchill, Duchess of Marlborough, the favourite and confidante of Queen Anne. For over a century it served as the London residence of the dukes of Marlborough. It became a royal residence through the 19th century and first half of the 20th. The house was expanded for the Prince of Wales, the future king Edward VII, and became closely associated with the prince in the Victorian era. Queen Mary lived there when she was Princess of Wales and took a special interest in the house; she returned to live there in her widowhood. The building was leased by Queen Elizabeth II to the Comm