14 (UPI) --Documents newly declassified by MI5, Britain's internal intelligence agency ... only told her about the infamous Cambridge Five member and art historian, Anthony Blunt, who was employed as the monarch's surveyor of official pictures, in 1973 ...

Anthony Blunt, who worked at Buckingham Palace as Surveyor of the Queen’s Pictures, was secretly a Soviet spy during WWII.

Queen Elizabeth II was not officially informed for almost a decade that one of her most senior courtiers had confessed to being a Soviet spy, according to newly released MI5 files.

Anthony Blunt, a royal art historial, confessed in 1964 to spying for the Soviets, but the late queen was not officially told about his past until 1973. View on euronews

Recently declassified MI5 files have shed light on one of the most infamous chapters in Cold War espionage, revealing previously hidden details about Soviet infiltration in Britain's intelligence establishment and the royal household.

When the Queen was finally told the full story in the 1970s, she was characteristically unflappable - taking it "all very calmly and without surprise".

Queen Elizabeth was left in the dark for almost a decade over the full scale of the treachery of one of her most senior courtiers, according to newly-released official files

The files about royal art historian Anthony Blunt are among a trove from the intelligence agency MI5 released Tuesday by Britain’s National Archives.

Queen Elizabeth II wasn’t told details of her long-time art adviser's double life as a Soviet spy because palace officials didn’t want to add to her worries, newly declassified documents reveal.