The following day he procured an invitation for Philip to lunch aboard the royal yacht. According to the account penned by governess Marion Crawford, Princess Elizabeth asked Philip what he would like to eat. Philip proceeded to gobble down several plates of shrimp and a banana split. In her book of memoirs about Philip, Queen Alexandra of Yugoslavia (formerly Princess Alexandra of Greece) says that years later, when the Queen and Prince Philip were trying to recall their meeting, she heard Philip say to the Queen: ‘You were so shy. I could not get a word out of you.’

In any event, it seems that Prince Philip made a favourable impression on the young Princess Elizabeth and an exchange of correspondence began between the two of them. No one can remember exactly when, but no doubt Marion Crawford prompted Elizabeth to write a letter of thanks to Philip for entertaining her and her sister during the royal visit and the distant cousins continued their correspondence throughout the war years.

Princess Alexandra wrote in June 1941 that when Philip was on shore leave in Cape Town, she found him writing a letter. ‘Who is it to?’ she asked. ‘Lilibet . . . Princess Elizabeth in England.’ Alexandra surmised that Philip was angling for invitations and she may have been right. By October that year, Philip had spent the first of several leave weekends at Windsor Castle. King George VI wrote to Philip’s grandmother Victoria Milford Haven: ‘Philip came here for a weekend the other day. What a charming boy he is and I am glad he is remaining on in my Navy.’

On one of his Windsor weekends, he and David Milford Haven (later to be his best man) rolled back the carpets three nights running and took the sisters Elizabeth and Margaret for their partners, treating them as though they were grown-up ladies of fashion in a London ballroom, instead of two schoolgirls incarcerated in an ancient castle with thick stone walls surrounded by wire. But, however gloomy Windsor Castle might have appeared to others, they loved the place. ‘Lilibet and I loved Windsor the best of all our homes,’ Princess Margaret later recalled. ‘It has such atmosphere.’

Prince Philip obviously liked it too as, despite dismissing his time there with typical insouciance, he spent several spectacular Christmases there with the royal family. The King and Queen had some concerns – not because they didn’t like Philip, because they did, but they thought their daughter was too young to become too involved with anyone, let alone someone as dashing and macho as the virtually penniless prince.