Once, when they were staying at Balmoral, Lady Adeane, the wife of the Queen’s private secretary, gave them a paper bag full of mushrooms she had just picked. A row quickly ensued over who was going to present them to their mother. They started tugging at the bag, which burst open, spilling its contents over the gravel drive – at which point Anne, who had just returned from a riding lesson, set about her brother with her riding crop. Charles burst into tears just as the Queen opened the door. In exasperation, she shouted: ‘Why can’t you behave yourselves!’ and boxed them both around the ears.

As the princess admitted: ‘We fought like cats and dogs.’ And ‘no’ was not a word she readily responded to. ‘When she got really worked up, she would start throwing things at him,’ Mrs Parker said. ‘She was very strong-willed, a real menace.’

She was forever ignoring her nanny’s instructions not to take too many toys out, but would instead empty the entire cupboard onto the floor and, in those days of coal fires in every room, make herself ‘filthy in the process’. If she didn’t get her way ‘she had the most frightful fit of temper, lying on the floor and kicking with sheer temper’.

Charles was surprisingly nice to his boisterous little sister (‘perhaps too nice,’ Mrs Parker observed), always inviting her to join in his games, taking a concerned and conciliatory attitude towards her excesses. And for all their squabbles, the two got on reasonably well together, as they had to. For, like their mother and her sister before them, Charles and Anne spent more of their infancy in the company of adults – servants, courtiers, family members – than they did with children of their own age and it was to each other that they turned for playful companionship. That happened to suit Charles, who did not mix easily.

But if Anne was more than her brother’s equal, it was Charles who commanded the greatest attention, no matter what their father might have thought about his abilities. He was born to be king and that fact was subtly drummed into him and his sister from their earliest memory. By her own account, she ‘always accepted the role of being second in everything from quite an early age. You adopt that position as part of your experience. You start off in life very much a tail-end Charlie, at the back of the line.’ And however much she might kick and scream, there, by genetic accident and the law of primogeniture, she was destined to remain.