Some previously unseen sensitive documents have claimed that a communist spy once tried to infiltrate the British monarchy by making contact with Queen Elizabeth II's brother-in-law.

According to documents recently released by the then-Czechoslovakian StB secret police, a Czech secret agent tried to infiltrate the Royal Family during the Cold War. Captain Bohumil Karkan, who went by the code-name Krupsky, is said to have met Lord Snowdon twice in the 1970s, reports The Sun.

Krupsky posed as an embassy official to meet Antony Armstrong-Jones, the 1st Earl of Snowdon, who was married to the queen's sister Princess Margaret back then. The royal agreed to meet the agent at his and Princess Margaret's home in Kensington Palace, and also gave him his phone number.

During the meetings, the secret agent reportedly discussed an upcoming Royal trip to the Soviet Union by Prince Philip and Princess Anne in 1973, where the father-daughter duo attended the European Horse Trials. Krupsky also talked about a possible photo exhibition with the British royal who was a professional photographer. Lord Snowdon, who had previously visited the Soviet bloc, asked the agent about getting his photography exhibition into Czechoslovakia.

According to the documents, Krupsky described one of their meetings to have a "friendly atmosphere, which created conditions for further social contact." It is also suggested that the royal never realised the man was a spy, and never colluded with the communist agents.

Buckingham Palace, the official residence of the queen and the Duke of Edinburgh, has not commented on the report.

This was not the first time that the royal family was exposed to Communist spies, most notably by Anthony Blunt, a member of the Cambridge Five spy ring. Initially recruited by NKVD (People's Commissariat for Internal Affairs- a government department in the Soviet Union), Blunt had joined MI5 at the start of the war, from where he passed intelligence on to the Soviets.

After working as a spy for several years, he refocused on his career as an art historian and even became Surveyor of the Queen's Pictures gaining access to Buckingham Palace. He also received a knighthood for his work in the expansion of the Queen's Gallery and continued in his post even after admitting to having been a spy in 1964. The entire controversy was covered in the hit Netflix series "The Crown" as well.

He was finally stripped of his knighthood in 1979 when he was exposed as a spy. The incident took place six years after he retired from Buckingham Palace.

Antony Armstrong-Jones
Princess Margaret and Antony Armstrong-Jones stand in the grounds of Royal Lodge on the day they announced their engagement on 27 February 1960 Getty Images