OPINION: The date: November 1996. The place: Diana’s private apartment at Kensington Palace. The scene: two women sitting opposite one another on plush settees, drinking iced water served by a butler and discussing life, love, marriage, and divorce.

“This is a new life,” the Princess says, smiling. “A new regime, with new rules. I’m grown-up now: I just want to be treated that way.”

Shockingly, nine months later, she would be killed in a car crash in Paris.

The Princess and I were having one of our catch-up chats which – although obviously offering me only one side of the story – helped me piece together the state of mind of the most famous woman of her generation.

In a few days’ time, the world will be treated to another version of Diana. Elizabeth Debicki, the accomplished Australian actress, will re-enact the final weeks of the Princess’s life in the final season of The Crown. The Netflix series will also – with exceptional bad taste – bring Diana back from the dead to appear as a ghost before both Charles and the late Queen.

Debicki has spent long hours studying footage and photos of the Princess. She has perfected her voice and many of her mannerisms. But how can you capture the essence of a woman you have never met? One of the problems with portraying someone who lived so recently is that there are lots of people, like me, who did know Diana and who find Debicki’s valiant effort sometimes unconvincing.

The Princess was tall, and proud of it, but not over six feet tall like Debicki, who seems to stoop in a rather self-effacing way as she towers over those around her. She was thin like Debicki – indeed, early in her marriage she was emaciated – but towards the end of her life, she was strong, toned, muscular and fit. She did indeed have a habit of cocking her head to one side and looking, doe-eyed, through her lashes. But not all the time. The Crown exaggerates this – just as it embellishes or imagines so much about the royals.

In her later years, the Diana I knew would look you straight in the eye. She was confident and, as she told me – all grown-up. For example, she said she had successfully taken control of her divorce negotiations. “I took advice from Mark Phillips and Tony Snowdon.

They both told me to make sure everything was settled before I signed anything. But the Palace kept trying to get it all through before the details had been decided. That’s why I threatened to pull out of the negotiations altogether.” She smiled ruefully. “That did the trick!”

She was shrewd. She told me that she’d received a “pompous” letter written by one of the Queen’s senior courtiers (whom she named). It had appalled her. And she was keeping hold of it “in case she ever needed it”. Diana was nobody’s fool.

But what is missing more than anything in The Crown is her soul: her charisma, her sparkle and her wicked sense of humour. She found great joy and fun in life, as well as sadness and disappointment. She told me that she didn’t wake up every morning thinking: “Yippee! I am the most famous woman in the world!” But she loved it when people yelled out to her “Lady Di!” It was, she thought, a term of great affection. And she found it hilarious that, having been so pampered in her royal life, she had completely forgotten that you had to put fuel in the car after dispensing with her police protection and drivers. “I went downstairs and jumped in …and it was empty!” She laughed that girlish giggle, head thrown back, as she happily took the mickey out of herself.

It was part of her innate charm. Men and women found her bewitching, and she was well aware of the power that gave her. She was far from the shrinking violet we sometimes see in The Crown.

Diana was a complex character, badly damaged by her parents’ divorce and her own broken marriage. At times she did indeed feel and behave like a victim (which The Crown accurately depicts) but in that final year or two, she struck me as far more of a pragmatic realist. She had apparently come to terms, as much as any wife could, with the fact that her husband had loved someone else.

“Let’s face it,” she said as we sipped our iced water. “Camilla is the love of Charles’s life, and always has been. I don’t feel any animosity towards her any more. In fact, I really think she deserves some form of recognition. After all, she’s been loyal to him and extremely discreet for such a long time.”

If it was genuine, it was a magnanimous gesture from a woman who was finally resigned to a situation she couldn’t change and who had decided to move on. I asked her what she meant by “recognition“ for Camilla. Did she mean marriage?

“No, not necessarily,” she said. I’m not sure what kind of recognition, but I don’t really see any need for them to marry.”

As the new episodes of The Crown unfold, perhaps its writer Peter Morgan will have Diana’s ghost musing on the state of her ex-husband’s very successful marriage. Perhaps we shall also hear her imagined verdict on his new role as King – a job for which she declared him unsuitable both on Panorama and in my conversations with her.

“He’s having enough problems being Prince of Wales”, she insisted to me. “He really couldn’t handle being King. Anyway, I honestly believe he’d be far happier living in Italy, painting and studying architecture.”

In the 26 years since Diana’s death, I have been surprised by how rapidly her universal fame faded. Once, the simple name Diana was all you needed almost anywhere in the world to ignite sometimes hysterical interest in the fairytale Princess. And if you told anyone you had known her, they would be in awe. But, as the years have passed, I’ve suddenly found myself having to explain who she was. A new generation has grown up knowing little about the Royal Family, and probably caring even less. Until that is, Netflix launched The Crown.

It is, of course, a highly polished production with a starry cast and dramatic script. But it is a work of fiction, rooted so skilfully in real events that the truth becomes blurred. And, in my experience, far too many young people believe every word that springs from Morgan’s fertile imagination. That, I think, is unfortunate – particularly when the events depicted are so recent and so painful for those who were directly involved or those who lived through them.

Diana was many things to many people: wronged wife, heroine, crusader, lover, paparazzi prey. To capture all of this was probably an impossibility from the start. And perhaps it should never have been attempted. Because to the two people who knew her best of all, William and Harry, she was simply Mummy. And to see her final weeks and her death paraded on TV for the pleasure of a worldwide audience is, in my view, cruel beyond measure to her sons.