Vanity Fair/Mario Testino
All three left their homelands or their social circle to become the independent, international icons of popular imagination. They were in a sense voluntary exiles, finding themselves in spite of their backgrounds and careers and in the process shattering the existing iconography surrounding them.
Thus Grace Kelly left behind a successful Hollywood acting career to marry Prince Rainier of Monaco, former First Lady Jackie O earned the approbrium of sophisticated American society when she married the rough-hewn Greek shipping tycoon, Aristotle Onassis while Diana's decision to engineer a separation and subsequent divorce from Prince Charles plunged the Crown into its biggest crisis since the 1936 Abdication.
By the time of her death in 1997, Diana was moving further and further away from the English upper classes with whom she had always felt ill at ease. She was moving West, spending more time on the East coast of America, mixing with movers and shakers in New York and Washington. Colin Powell, Henry Kissinger and Anna Wintour, editor of Vogue, were occasional dinner companions. She liked the idea that she was a princess for the world rather than the Princess of Wales.
Like Grace and Jackie, she was becoming sleekly international both in her fashion style - in her last photo shoot Mario Testino perfectly captured that informal charisma - and the causes, notably the International Red Cross which she espoused.
She had a role model of sorts in her mother Francis Shand Kydd who cut herself off from polite society after her acrimonious divorce from Earl Spencer. She found solace living anonymously on the north west Scottish coast.
During her own lifetime, Diana, post divorce, found history repeating itself. The English aristocracy no longer welcomed her into their salons quite so freely as they once did in spite of her popularity. Frozen out of enough polite society to make living in England something of a social chore, she was drawn increasingly to, what she believed to be, the egalitarian social whirl of America. Of course American society, as Jackie O discovered, is as closely knit and tightly structured as anything that the English aristocracy can conjure up but to a natural outsider like Diana she was not bound by those strictures and structures.
At the time of her death she was looking for romance, searching for a partner who would anchor her and give her the baby daughter she craved. Much has been made of her summer love affair with Dodi Fayed, a romance engineered and executed by his father, billionaire businessman Mohammed. Those who knew her at the time believed the fling was fizzling out - the look of tired exasperation on her face as she left the Ritz hotel in Paris before that final journey is bleak testament to that witness.
No, she was looking West for inspiration and for consolation. The name of billionaire Teddy Forstmann was in the frame that fateful summer. She and her boys were due to stay at his home in the Hamptons. For some reason the trip was canceled - some later speculating that it was because of 'security concerns.' Those concerns led her into the embrace of the Fayeds and ultimately the Alma tunnel in Paris.Had she lived she would have celebrated her birthday watching TV, looking on as William and Catherine perform their first joint overseas engagement in Ottawa. She would probably have been in New York, possibly the Hamptons where she now had her own estate - after all she received $25 million from her divorce settlement. While not quite the puppeteer, she would be looking carefully to see if Catherine, whom she had taken under her wing, was following her advise on how to deal with the big public events. Not that Catherine, who has taken to the spotlight as if to the manor born, has needed much quiet coaching.
While there would have been relief that at last the focus was moving to a new generation - and good riddance to the ever present grim-faced paparazzi 'courtiers' - there would have been a feeling too of what might have been just as there was for the Duke of Windsor when he saw his younger brother take the throne in his stead and represent his country.
As she turned 50 she had given up the chance to become queen. She would instead be representing not the House of Windsor but herself on the world stage, a global icon, unique, charismatic and seemingly indestructible. A woman who would surely have gathered more more Facebook followers than the Queen.
View gallery: Diana at 50 - A Look Back at The People's Princess