LONDON — Queen Elizabeth II was not formally informed of the betrayal of a senior courtier for nearly a decade, newly declassified documents show.

Anthony Blunt serves as the royal family's chief art curator, responsible for surveying the Queen's paintings, overseeing the royal collection of paintings and occasionally displaying her private treasures to the public. He was so beloved by the Queen that he was knighted - despite leading a double life as a Soviet spy.

Britain's National Archives released a trove of documents from Britain's intelligence agency MI5 on Tuesday that shed new light on a Cold War scandal at the heart of Britain's power establishment. The saga has long fascinated historians and figured prominently in pop culture, from spy novels to Netflix's The Crown.

Documents show Blunt admitted in 1964 to spying for the Soviet Union as a member of the notorious Cambridge Five, but it was not until 1973 that the Queen learned the full story, and her reaction was calm and unsurprising. His true identity was eventually revealed to the public by former British Prime Minister Margaret Thatcher in a speech in Parliament in 1979.

Given Blunt's prominence, security services closely guarded his identity, with only a handful of senior officials privy to it, although the secret may have been known. The Queen's private secretary, Martin Charteris, was only told that MI5 intended to interrogate Blunt because of his close relationship with fellow spy Guy Burgess, who had fled to the Soviet Union.

Historian Chris Smith, who has written a biography of Cambridge Five Nations spy John Cairncross, said the events likely "told us more about the state's inability to prosecute Blunt" than about military intelligence Five agencies worked together to keep the late Queen in the dark. told NBC News.

"Informing Her Majesty or anyone else about this could be defamatory; it could also be considered embarrassing to Her Majesty," Smith said.

Smith added that Blunt had also become the consummate establishment figure when it was revealed he was a spy, which was "very embarrassing" for the royal family.

Therefore, withholding this information "would also allow the Crown to truthfully deny that Her Majesty had any knowledge of Blunt's espionage activities, thereby sparing her personal embarrassment."