Princess Diana's influence on the royal family lives on

Fifteen years on, Diana's memory has faded but she can be credited with the Queen's Olympic cameo and much more
People stand in front of the Flame of Liberty statue in memory of Princess Diana in Paris
People stand in front of the Flame of Liberty statue in memory of Princess Diana in Paris. Photograph: Gonzalo Fuentes/Reuters

Fifteen years ago this morning my wife woke me at 6am with an uncharacteristically robust thump: Princess Diana had been killed in a car crash in Paris after trying to escape the paparazzi in the company of Dodi Fayed. Melodramatic and tacky, it was in that dawn moment close to being that over-used word: unbelievable. "Is it really true?" people later asked each other on the tube as they read the shocking newspaper headlines.

It was indeed, and the royal family fell into its gravest crisis since the abdication of the Queen's uncle, Edward VIII, in December 1936. Its response to Diana's death was inept and seemingly callous. If the House of Windsor was saved by the shrewder "people's princess" instinct of its new prime minister, it was not grateful: neither Tony Blair nor Gordon Brown was invited to last year's royal wedding.

But the Windsors have recovered and Di's memory – once so vivid, often so radiant but also wretched – has faded, as wise hands knew it would. How many anniversary articles to mark her death in 1997 did you read today? I had forgotten it myself, though at a Guardian lunch I once sat across the table from her. You don't forget that.

Yet Diana's posthumous influence on the royal family lives on in significant ways, irritating though it must be to be reminded of it. She forced them to raise their game, she enlivened their Hanoverian gene pool.

In a series of initiatives to "detox" the brand, the Queen and her family have engaged in a series of informal gestures to ease the unbending and remote image which the late Elizabethan age had acquired and Prince Charles, in his frustrated waiting-room prime, had failed to dispel – by virtue of his temperament and constraints. The party at the palace, the Queen's Olympic cameo … they and much else would once have been unthinkable.

But Di – none of this Diana, Princess of Wales stuff in the new era – also bequeathed the Windsors her sons, the heir and the spare. Even royal watchers like Penny Junor, whose new biography charts the lives of the Duke of Cambridge and his bride, do not really tell us what Prince William is like. His privacy is well guarded and he apparently likes it that way.

William shares Lord Justice Leveson's distaste for the press but, perhaps unlike Leveson, is more realistic about dealing with it. Those supermarket photos in north Wales suggest he knows the need to feed the beast. He cannot leave the PR department all to brother Harry and his well-documented wild side.

So much has been written about Diana that it becomes harder to unpick it all. Is she fated to become a tragic female icon – the beautiful princess of the fairytale who had everything except true love and happiness – like Marilyn Monroe into whom hopes, dreams and theories are poured? Surely a serious artist will eventually write a play, an opera even, to re-evaluate and explain the drama of her life?

On the day she lunched at the Guardian editor's table the thing that struck me most was how smart she was. Here was a woman with little serious education who had been plucked from her life as a "Sloane ranger" nursery nurse at 19 because her aristocratic pedigree and blameless private life fitted the dynastic imperative. Yet she was quick, shrewd and funny – as well as glamorous. Of course.

The occasion must have been part of her post-divorce media offensive; chat to the editors, get them on my side, that sort of thing. She had a PR person with her, but there was no need. She didn't put a foot wrong as she parried questions, some of which were designed to lure her into indiscretion. Of course the boys had to go to Eton, to be near their grandmother. No, Charles and I never disagreed over the children. She wasn't mean or gloomy, she was good company.

Two specific things I remember. She came closest to malice when asked about Princess Anne's charity work. "Just reading about it in the court circular tires me out," was roughly her reply. And when explaining how the paparazzi could get more money for their photos if she was seen to weep she said they could be abusive – "they use the F-word". No one else present remembers that phrase, but I'm sure she used it.

Was the moment of delicacy all part of the image? Of course. Even then we all had an inkling of how manipulative she could be. Now we understand more about mood swings and bulimia, about her troubled childhood, the toll it had taken and the inadequacy of the buttoned-up Windsors' efforts to deal with it.

After the lunch Guardian staff crowded to the windows to spot Di leaving, among them Peter Postance, a genial ex-printer. Walking past him, so I was later told, the princess tapped him on the shoulder and asked: "Looking for anyone?" That's why she was popular.

Someone leaked to the Daily Mirror a passing remark she had made about what a nice man Blair seemed to be (the then opposition leader and Alastair Campbell had also been targets of Di's charm offensive). But apart from that glitch the event went off without incident or much consequence for the paper's editorial stance. Afterwards I thought: "This can't last". And it couldn't. Sixteen months later she was dead.