Visitors attend the preview of the exhibition Lady Diana a Free Spirit at the Reggio di Venaria, northern Italy. Picture: AP

London - As the 20th anniversary of the death of Diana, Princess of Wales, approaches, her former private secretary Patrick Jephson has decided that the time is right to berate the Royal Family for a failure to treat her with the humanity and respect she deserved.

In a new American edition of his book Shadows Of A Princess, Jephson writes: "Remembering Diana . . . can be summed up in one word — a word traditionally synonymous with the British Crown, exemplified by Elizabeth II’s lifetime of service.

"The word is decency. Yet in some corners of the royal establishment, two decades of spin doctors and a naive fondness for the slippery arts of news management have put the word and the idea at risk . . .

"Diana alive was a decency test for the Windsors, which some of them failed."

Jephson, a former Royal Navy officer who served as her private secretary for eight years, refrains from naming which Windsors he has in mind.

However, his new introduction to his book turns the spotlight in an unmistakable direction.

"With his Coronation plans already the subject of unfriendly speculation, especially on the divisive issue of Queen Camilla," writes Jephson, "Elizabeth’s successor faces an acceptability hurdle that some courtiers may be slow to recognise. A little perspective from recent history might guide them."

Jephson, now a naturalised US citizen, rams home the point, arguing that Diana, feeling "ill-prepared and untrained for the role in which she found herself", believed she had been "left to sink or swim".

He continues: "Her private life offered no consolation, with a husband who . . . saw her as a rival to be feared rather than a companion to be cherished."

Charles’s "energy, time and attention were devoted to the older, more experienced wife of a former courtier who, like many of their secretive social circle, seemed impervious to the vulnerable princess’s anguish.

"No wonder Diana suffered from chronic self-doubt, poor self-image and a persistent eating disorder."

Some may wonder whether Jephson himself has failed the decency test. In 2000, he was accused of "betrayal" for publishing his book about his time in Diana’s service.