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FILE - Harold "Kim" Philby, one of the Cambridge Ring of Soviet Spies, Aug. 11, 1955. (PA via AP, File)

FILE - Harold "Kim" Philby, one of the Cambridge Ring of Soviet Spies, Aug. 11, 1955. (PA via AP, File)

FILE - Professor Anthony Blunt, former surveyor of the Queen's pictures, photographed at the Courtauld Institute on Nov. 15, 1979. (PA via AP, File)

FILE - Professor Anthony Blunt, former surveyor of the Queen's pictures, photographed at the Courtauld Institute on Nov. 15, 1979. (PA via AP, File)

FILE - Professor Anthony Blunt, former surveyor of the Queen's pictures, photographed at the Courtauld Institute with Queen Elizabeth II on Nov. 15, 1979. (PA via AP, File)

FILE - Professor Anthony Blunt, former surveyor of the Queen's pictures, photographed at the Courtauld Institute with Queen Elizabeth II on Nov. 15, 1979. (PA via AP, File)

FILE - clockwise from top left, Anthony Blunt, Guy Burgess (who died in Moscow in 1963), Donald MacLean and Kim Philby, who tipped off Burgess and MacLean in 1951 forcing them to defect and then defecting himself in 1963. (PA via AP, File)

FILE - clockwise from top left, Anthony Blunt, Guy Burgess (who died in Moscow in 1963), Donald MacLean and Kim Philby, who tipped off Burgess and MacLean in 1951 forcing them to defect and then defecting himself in 1963. (PA via AP, File)