51°30′18″N 0°8′9″W / 51.50500°N 0.13583°WMarlborough House, a Grade I listed mansion on The Mall in St James's, City of Westminster, London, is the headquarters of the Commonwealth of Nations and the seat of the Commonwealth Secretariat. It is adjacent to St James's Palace.
The house 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 and his social circle in the Victorian era. His daughter in law, later Queen Mary, lived there when she was Princess of Wales and took a special, continuing interest in the house; she, like her mother-in-law Queen Alexandra before her, returned to live there in her widowhood and memorials to both queens are on its grounds. The building was leased by Queen Elizabeth II to the Commonwealth Secretariat beginning in 1965.
