For Prince Charles, however, there was no such escape. He was a prisoner of his position and he had to find a suitable wife, with every move he made closely scrutinised by the press. He eventually did – in the gangling, teenage form of a local Norfolk girl, who also happened to be a family friend and the granddaughter of an earl. Lady Diana Spencer was young, she was a potential beauty and, most important of all, she was unsullied by any sort of scandal or romantic past, as most of Charles’s previous girlfriends had been.

In November 1980, while Diana was visiting Sandringham as their guest, the press interest in her peaked and photographers surrounded the estate hoping to get a picture or at least a sighting. It bothered the Queen, who was both irritated and worried by the attention being caused by Diana’s presence at the big house. She was uncomfortable with it but characteristically said nothing to Charles directly, but instead discussed it with Philip, who wrote their eldest son a carefully considered letter. Media pressure was creating an intolerable situation, said Philip, which meant that Charles must come to a rapid decision. Either he must offer Diana his hand or he must break off the relationship to avoid compromising her reputation.

‘Read it!’ Charles would furiously exclaim to friends in later years, whipping the letter out of his breast pocket. ‘It was his attempt to say that he was forced into the marriage,’ recalled one who saw the note. However, another who read it confided: ‘It was actually very constructive and trying to be helpful. It certainly did not read as an ultimatum.’

On 24 February 1981, Prince Charles announced his engagement to the twenty-year-old Lady Diana Spencer. She was the youngest daughter of Viscount Althorp and his wife, Frances Shand Kydd, and the maternal granddaughter of Lady Fermoy, who was a friend and lady-in-waiting to the Queen Mother. Diana’s father, later the 8th Earl Spencer, had served as an equerry to the Queen between 1952 and 1954 and to George VI for the two years before that. The family lived at Park House on the Sandringham estate and the Queen had known Diana fleetingly most of her life. Diana’s elder sister Sarah had been a girlfriend of Prince Charles’s and her other sister, Jane, was married to Robert Fellowes, the Queen’s assistant and later her private secretary.

‘She is one of us,’ the Queen wrote to a friend. ‘I am very fond of all three of the Spencer girls.’ Whether or not she realised the troubles brewing with Diana during the months leading up to the wedding, she chose to ignore them.