Known as Sir Anthony Blunt, KCVO, from 1956 to 1979, was a leading British art historian who in 1964, after being offered immunity from prosecution, confessed to having been a Soviet spy. A closely held secret for many years, his status was revealed publicly by Prime Minister Margaret Thatcher in November 1979, and he was stripped of his knighthood immediately thereafter. Blunt was Professor of the History of Art at the University of London, director of the Courtauld Institute of Art, and Surveyor of the Queen's Pictures. He was exposed as a member of the Cambridge Five, a group of spies working for the Soviet Union from some time in the 1930s to at least the early 1950s.