Which elegant royal joined the Hitler Youth, dropped her pants for the head of the CIA - and claimed as an excuse: 'My diplomats are, by and large, bunglers and fairies'?

She was a one, that Queen Frederica of Greece! 

On a visit to Washington DC she brought a whole new meaning to the phrase 'entente cordiale' when Her Majesty was caught with her pants down having sex with the head of the Central Intelligence Agency.

The Queen, a cousin of both Queen Elizabeth and Prince Philip, was in Washington to strengthen Greco-US relations in the late 1950s and, it can fairly be said, her trip was a resounding success. 

Just as the visit was about to end, she announced without explanation she'd stay on for another week.

She'd come to Washington to discuss 'spiritual values' with President Dwight D Eisenhower in the Oval Office and afterwards was sent to visit spy boss Allen Dulles at his CIA headquarters.

'They had been alone in his office for nearly an hour when an aide knocked,' wrote former New York Times correspondent Stephen Kinzler.

'Hearing no response, the aide entered. He found the office empty, but heard noises from the adjoining dressing room. Later Dulles and the queen emerged from this sanctum in a state which indicated they had been engaged in intimacy.' 

In fact Dulles, a notorious womaniser, had had a day-bed specially installed in the dressing-room so he could take 'naps'.

As she was being driven back to the Greek Embassy, Frederica turned to her driver and triumphantly declared the reason Greek-American relations were so strong was due entirely to her irregular sex life – she was still married to husband King Paul - 'I just love that man!” she exclaimed, and she wasn't talking about Paul.

'My diplomats are, by and large, bunglers and fairies,' she declared in justification for seeking her one-to-one relationship with Capitol Hill. But against her own country's best interests she urged Dulles to spread his CIA spies across Greece

Unsurprisingly Frederica, granddaughter of Kaiser Bill and great-granddaughter of Queen Victoria, was an unpopular figure, especially back at home. She'd been a member of the Hitler Youth during her teenage years in Austria and was considered to be dangerously right-wing. She pulled her son's – the future King Constantine's – strings with considerable force.

On a trip to London in 1963 she and our own Queen, Elizabeth II, were booed by a hostile crowd as they went to the West End theatre- the only recorded time Lilibet was treated so antagonistically. 

So worried were the Foreign Office that the protestors might get into the Aldwych Theatre and disrupt the play, they bought up all 1,100 seats for that night's performance.

The officials had good reason - during a previous London visit only a few months earlier, Frederica had been spotted and chased down the street by demonstrators opposed to the Greek government's repressive regime - which had been endorsed by the queen - and had to take refuge in the house of a complete stranger.

But being caught with her pants down didn't bother Her Majesty one bit – in her 1971 memoirs, Frederica boasted of her closeness to her 'old friend' Dulles, a notorious womaniser but a man whose snobbery could not resist a woman capable of tracing her ancestry back to the 18th century King Frederick the Great of Prussia, after whom she was named.

Frederica was a great-granddaughter of Queen Victoria a member of the Schleswig-Holstein-Sonderburg-Glücksburg dynasty, to which Prince Philip belonged.

Her daughters were Sofia, now Queen of Spain, and Irene of Greece. Her son was King Constantine II of Greece.

Frederica – Freddie to her family – fell victim to her own machinations when the military junta which ran the country deposed the royal family in 1973. 

 Constantine had inherited the crown on the death of his father in 1965, but despite repeated attempts to restore monarchy to his country, spent most of the rest of his life in Britain, a welcome guest at Buckingham Palace at all times but a king without a throne.