Twenty years in August since Diana died. The anniversary is sad for me on many levels — she was definitely the final famous person I’ll have a pash on, and it reminds me that I haven’t yet earned back the whopping advance I was given for my book about her. To be fair, the book was an absolute stinker, written through a haze of gin, tears and avarice, containing such clodhopping clangers as ‘with blue skies in her eyes and the future in her smile’ and ‘affection swooshed out of her like a firework from a bottle’. Nurse, the screens!

But there was good stuff in it, too. Namely, the way I served it to the Prince’s Party who continue to curdle Diana’s memory much as they tried to ruin her reputation during her lifetime. There can be little doubt that Diana was comprehensively ‘gaslighted’ by her husband and his mistress during the early part of her marriage, when she was at her most hopeful and vulnerable. Diana’s Ophelia Years, when she was forever mauling at herself with kitchen utensils and bringing back her breakfast, make sense in the light of this carefully choreographed cruelty.

It was the Tory MP Nicholas Soames, most gruesome of the prince’s groupies, who opined that Diana was in ‘the advanced stages of paranoia’ after her piquant hat-tip to Camilla that ‘there were three of us in this marriage so it was a bit crowded’. Twenty years on, we hear the same geek chorus carp whenever Diana’s name is mentioned ‘Oh, she was no saint! She had a temper! She was spiteful! She had lovers!’

That’s the stuff I liked about her — the tantrums, the threats, the malice, the affairs. A woman who is all goodness is as insipid as a Bloody Mary without Tabasco. Even when Diana was embarrassing — before she grew into the cool customer who could look down and laugh at the out-of-time Windsors from her winner’s podium on the world stage — it was with a cringiness most of us have been guilty of to some degree. These were the Bridget Jones Years, when she was every needy, Mills & Boon spoon-fed, nightmare girlfriend, seeking from men the comfort she had failed to find from either her first family (the Spencers) or her second (the Windsors).

The subsequent Bunny Boiler Years were not her finest, especially when it was revealed that she had been a cold-calling, heavy-breathing sex-pest, subjecting the unfortunately named and inconveniently married art dealer Oliver Hoare to 18 months of nuisance phone calls, sometimes as many as three in 15 minutes. But what woman who had ever been prey to thwarted passion didn’t secretly want to high-five her? He probably led her on, the rotter!

When a bunny boiler becomes bored by her own emotional incontinence, she becomes a bitch, if she’s lucky. Diana’s Bitch Years were majestic. She was the toast of the New World by then, and from the distance of Manhattan could treat the Windsors like the provincial cheese-parers they are. She kept her evil twin happy by taunting her ex-in-laws, probably reaching peak-bitch when she called the Queen Mother ‘chief leper of the leper colony’.

In this week’s heartbreaking documentary by her sons about their mother, Prince William recalled: ‘One of her mottos was: “Be as naughty as you want, just don’t get caught.” She was one of the naughtiest parents.’ Whether up to something as simple as assisting her sons to smuggle sweets into school in their socks, or as worldly as lining up a hat trick of supermodels —Christy, Cindy, Naomi — to greet the adolescent Prince William when he arrived home, it’s clear that Diana’s sense of mischief was highly developed, and mischief held a beat too long — and informed by sorrow — can easily become devilment.

‘She won’t go quietly — that’s the problem,’ said Diana of herself in a moment so full of defiance that for once someone referring to themselves in the third person didn’t seem ridiculous. ‘I’ll fight to the end, because I believe I have a role to fulfil, and two children to bring up.’

In her final years, she had became a scenery eater of the coolest kind; this is the part of the Joan Crawford film when the heroine finally realises that her man done her wrong and her fresh, ingenue face turns into a hard-smiled, glittery-eyed mask for a moment before she snaps back to normal — or at least what passes for it: ‘From now on it’s just me and the kids. And I’ll do anything for those kids. D’you hear me? Anything!’

So if you raise a glass to her next month, remember her this way: not Diana the Sacrificial Lamb or Diana the Mater Dolorosa, but Diana the Diva, goodness and badness perfectly enthroned in one shining spirit.