There was a dark personal side to this apparently blossoming public face. Bertie, now transmogrified into George VI, had always been prone to tantrums, known to his family as ‘gnashes’. The confusion and fear engendered by this dramatic change in his position and by the later worries caused by the war only served to exacerbate his unsteady and sometimes violent temperament. His father had been subject to similar temper fits. His married life was less than blissful, and King and Queen sometimes found it so difficult to communicate that they had to write letters to each other instead.

Late in his life, Edward VIII, then Duke of Windsor, told James Pope-Hennessy: ‘Off the record, my father had a most horrible temper. He was foully rude to my mother. Why, I’ve seen her leave the table because he was so rude to her, and we children would all follow her out.’ He then added, ‘Not when staff are present, of course.’ But staff have a way of finding out about such things. George V’s behaviour was well-discussed in the servants’ quarters, although scenes of such private unhappiness and frustration were never played out in public.

As far as it was possible to contain them, such outbursts were not allowed to intrude up onto the nursery floor. ‘We want our children to have a happy childhood which they can always look back on,’ Queen Elizabeth would insist. But the happy family idyll had been damaged. The family were forced to move out of 145 Piccadilly and into Buckingham Palace, a cold, impersonal building with endless corridors which could take a whole morning to navigate. Couldn’t they build a tunnel back to Piccadilly, Elizabeth wistfully suggested? But this new world, with its domestic upsets and feuds and subtleties of status and inexorable duty, could not be locked out. Bath time with their parents, always such a ritual, had to be cancelled because the King and Queen, who before had spent most of their evenings at home, were now out almost every night at official functions.

Princess Margaret, then six, and the older Elizabeth could not but be aware of the tensions and the strain events had caused their father, of the way their mother, once so relaxed and easy-going, now looked drawn and older. There had also been a change in Elizabeth’s own status. As a little girl, she had been taught to curtsey to her grandparents whenever she visited them. The aura of majesty had now fallen on her parents and she was instructed by Crawfie that henceforth they had to curtsey to Papa and Mummy.

‘Margaret too?’ Elizabeth asked.

‘Margaret also,’ was the answer. ‘And try not to topple over.’