Who was "the fourth man" in the Cambridge spy ring, whose name was not publicly known until 1979?

Question

As well as being a spy, for which brief career she was both celebrated and then executed, in what other profession did Mata Hari engage?

Answer 1

Anthony Blunt
Maclean and Burgess defected in 1951, and Philby in 1962. In November 1979, Prime Minister Margaret Thatcher admitted to the House of Commons that Blunt had confessed to being a Soviet spy in 1964 and had been granted immunity in exchange for information.