Ken Wharfe is not a man to mince his words.
He served as a royal protection officer for 16 years and, as we know from his intimate memoirs serialised in the Daily Mail this week, never shied away from spelling out what was what.
Neither, it seems, did his boss, Princess Diana.
Take, for example, when Ken first met her at Kensington Palace in 1986 after being asked to apply for the vacancy to look after Prince William and Harry.
"The first thing she said about her sons was: 'I don't envy you, Ken. They can be a bloody nuisance.'
"William, who was playing the piano, turned round and said: 'I'm not a bloody nuisance.'
"Harry stood on a small table with this vase of flowers and the vase goes over the floor.
"William starts laughing. She gets up and chases them out of the room. I still hadn't said a word.
"She came back in and said: 'I'm really sorry about that, Ken.' I thought: 'I can work with this'."
Ken, 68, chuckles as he says this. There was, he says, "never a dull day" working for the Princess.
Indeed, he can entertain for hours with some of the more hilarious moments in Diana's employ.
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Take the day she organised go-karts for the boys to ride around on at Highgrove.
"William masterminded sorting out a track down the back drive and through the vegetable gardens, but Harry wouldn't listen to his brother and carved up his father's golden wildflower field.
"Diana thought it was hilarious. We put it right as best we could.
"I remember about two weeks later, the Prince of Wales saying: "I hear you had a good weekend? You're not thinking of becoming the next Bernie Ecclestone [the motor-racing mogul]?"
Ken slips into an impersonation of Prince Charles, which knocks Rory Bremner into a cocked hat and, by all accounts, regularly reduced the Princess to fits of giggles.
Harry more like his mother than William
"If you stay long enough, you pick up their habits," Ken says. "But Harry is more like his mother than William is."
When Ken mentions Harry, his face softens. He was, it turns out, the favourite among Palace staff.
William tended to be sly, whereas Harry was much more open. You knew exactly where you stood with him.
"He was a very likeable individual who'd come and knock on the door, saying: 'Any chance of a fight? I'm bored. Can I play with one of your walkie-talkies?'
"William wouldn't do that. He'd always stand back. That was his nature. He was a slightly difficult child.
"You know how in a group of children there's often the odd one who doesn't quite fit the bill?
"William was one of those. That wasn't to say he was bad. He was just not like his brother. He was prone to being a bit wet.
"Everybody liked Harry because he was funny. William wasn't. That was his character and, of course, he knew exactly who he was.
"Why wouldn't he? He's at a palace where there are chefs, nannies, cleaners, drivers, ladies-in-waiting, dressers and he was always being told he was something special.
The princes' bond with the royal nanny
"Diana was very good at bringing [Harry] down to earth, along with the late Olga Powell [the loving but strict nanny who began to look after the boys when William was six months old].
"She really was a super nanny. She was a lady almost of a different vintage and very firm in her style.
"I remember her catchphrase to William many times was: 'William, I love you but I don't like you.'
"If she put a bowl of cereal on the side, William would hide it and when she asked: 'Where's the bowl?' he'd say: 'I don't know where it's gone. Maybe Harry's taken it.'
Harry was always the favourite with royal staff
"I think probably the cause of William's unease as a young boy growing up was that the attention from a lot of the staff was centred on Harry, rather than him.
"But what you see now with Harry is exactly what I thought would happen: he has become a popular individual because of his style and delivery."
Indeed, the increasing regard in which Harry is held needs little comment.
"From his tireless efforts for Help For Heroes to his work with another charity, Sentebale, supporting the vulnerable children in Lesotho, all is done with his mother's easy touch.
"Harry would make a remarkable king," says Ken. "But sadly that isn't going to happen."
'William needs to get rid of his bad attitude towards the media," he says.
"What killed Diana was the incompetence of the security that night in Paris. End of story.
"So what's his gripe? As I see it, the media has only been very supportive of him and his family. He needs to chill out.
"The fact is that both William and Harry need to capture the hearts of a generation who will eventually decide whether or not this family exists in 50 or 60 years' time. Diana understood that."
Ken shakes his head. "She'd have been a guiding light for William and Kate if ... " The sentence ends in a sigh.
Prince Charles struggled to deal with Diana's popularity
There is little doubt that Ken was hugely fond of the late Princess. It was, he says, impossible not to be. She was "engaging", "funny" and possessed of "a wicked sense of humour".
She was also, at times, a desperately unhappy woman, particularly in the years following her humiliating confrontation with Prince Charles and his then mistress Camilla at Lady Annabel Goldsmith's house in Ham, south-west London, in 1989, as described in the Mail on Monday.
"Not long before that night, we were up in Scotland with her mother [the late Frances Shand Kydd]," says Ken.
"She was a good leveller for Diana. They were talking about Prince Charles and her mother asked her: 'Do you still love him?' Diana said: 'Of course I do.' So her mother said: 'Well, you've got to work at it.'
"Diana really tried. I remember once after an engagement we arrived back at Kensington Palace as the Prince was getting into his car.
"He waved and said: 'Did you have a good day?' Again, he slips into his impersonation of Prince Charles.
"She said: 'Yes, it was fantastic, where are you going now?''' His voice is higher, breathless as he mimics Diana.
(Charles) "Going to do my churches in the City."
(Breathless again.) "Oh that'll be nice. You like all of that."
(Charles) "I know, but it's sooo boring."
(Breathless) "Well, do you want me to come with you?" Ken pauses. The merriment in his eyes vanishes as he once again impersonates the Prince.
"No, they'll only be interested in you."
There is silence as the impact of the Prince's snub reverberates. Poor Diana.
"The Prince didn't know how to deal with her popularity," Ken says.
"Diana made desperate attempts to try to put that right. They could have been the biggest double act in the world, but after that confrontation with Camilla and Charles she felt there was no return.
"It was beginning of the end, but where do you go after the Royal Family?
Diana's desperate attempts to find happiness
"In essence there was nowhere for her to go. Diana was desperate, and desperate people often do desperate things."
Indeed. Take, for example, the extraordinary night Ken found her on a rooftop terrace in London's smart Belgravia area, sitting on a milking stool under a copper pyramid . . . well, probably best let Ken explain.
"The Duchess of York had put her onto this so-called copper pyramid scientist." The word "scientist" is loaded with scorn.
"There must have been a thousand-and-one candles on that rooftop, along with this woman dressed in black and this large copper pyramid.
"There was a sort of window at the top of it opening into the sky at night. Diana was sitting on a cow's milking stool in the middle of it.
"She'd been there for about an hour-and-a-half. I said: 'What are you doing?' She replied: 'I'm told all the badness will go straight up to the apex of the pyramid into the unknown.'
"I told her she'd been watching too much Patrick Moore [the astronomer who presented the BBC's The Sky At Night].
"She asked: 'Do you really think so, Ken?' I said: 'Look, if it makes you feel better that's fine. I'm not worried about you sitting under a copper pyramid. I'm more worried about you being caught on a rooftop with all this candlelight going on. But, tell me, has it made you feel better?'
"She said: 'No not really.' We never went again." Again, he chuckles fondly. Stops. Thinks.
"There were so many so-called advisers who felt they were able to steer Diana through this misery."
One was Mara Berni [the late legendary owner of San Lorenzo restaurant, whom Diana christened "Mother Confessor"] who knew a tarot card reader.
The Princess would see this person once or twice a month. After each, this woman would write to Diana with her thoughts.
"Diana showed me four pages of foolscap that looked as if it had been written by a four-year-old. It was bull**** basically.
"Pure adulation. 'You are fantastic. You will find happiness in the future - no matter what you're suffering now - and people will love you for it, and one day you'll fly up to heaven.'"
"The Princess of Wales was a great catch for people like that. They weren't going to lose her by saying: 'You've cracked up. Get yourself sorted out.'
"I'd tell her she was wasting her money and that they were only telling her what they thought she wanted to hear.
"The advice she needed was from her friends, women like Kate Menzies [the youngest daughter of multi-millionaire John Menzies and one of Diana's closest girlfriends], who would tell her when she was in the wrong.
"But that wasn't always what Diana wanted to hear, so she'd ostracise them and buy into this jungle magic nonsense."
Ken shakes his head and sighs once more. You can't help but feel he'd give his eye teeth to turn back the clock and put some sense into Diana's pretty head.
He warned her time and again not to give up her police protection after separating from Prince Charles in 1993 and believes that had she heeded his advice, the terrible events of August 31, 1997, in that Paris underpass would never have happened.
"When I went back to see Diana after I resigned I said: 'Whatever you do, don't give up your security. You can change your name to Mrs Smith. You can go and live anywhere in the world, but you'll still be Diana, Princess of Wales. You cannot, unfortunately, just drift into obscurity.'"
But Diana did not listen. The one person in my view who could have saved Diana is the Queen,' he says.
"Diana genuinely loved her. If the Queen had said, 'I understand where you're coming from. My son can be difficult' - because that was the sort of conversation they had on a regular basis - 'but you can't get rid of your security', Diana would have bought that, and we wouldn't be sitting here now.'
"Here" is a restaurant in Chelsea where we meet following the publication of his updated memoirs, Closely Guarded Secret.
Ken points out why the subject of the book is anything but ancient history.
"In the past few months, Prince Harry has been talking openly about his love for his mother.
"Nearly two decades after her death, he and his brother are publicly recognising the importance of the role their mother played in modernising the Royal Family.
"There's a resurgence of interest in her which is why, I believe, this memoir is important because it's written by someone who was actually there," says Ken, who worked as Prince William and Harry's protection officer before heading Diana's team.
"There have been more than 80 books written since she died by people who never actually met her."
Diana's close bond with her protection officer
We now know they travelled together over the course of six years - sometimes even adopting the pseudonyms of Mr and Mrs Hargreaves to throw the media off the scent.
During that time she confided her deepest secrets to Ken, right down to the sex toy she carried with her on foreign trips.
Indeed, such was the closeness between the Princess and her bodyguard - who had been married for 13 years when they first met - that Diana even ironed his shirt.
This once led to the astonishing episode when a young Prince William pulled down the bath towel which was all Diana was wearing one day in the kitchen of her mother's cottage in Oban, leaving her standing there in front of Ken without a stitch on.
"You pass your eyes aside and think: 'Oh God, what's happening? Get me out of here.'"
"Then, her mother came in and I think her phrase was: 'Perhaps it's best you go get some more oysters.'"
Really? "Yes really."
No lustful peeps at Diana's bodywork? 'Certainly not.'
Ever tempted? 'Oh good God, no,' he says. 'That was the last thing on my mind.
'You couldn't have done the work if you were emotionally involved or got anywhere near saying: "I love her." But of course I was fond of her. She was fun.'
Indeed, two days after Princess Diana's desperately sad funeral Ken met up with his fellow royal protection officers in a wine bar in Victoria.
"I was upset. We were all upset," he says. "We couldn't believe Diana could have died in something as mundane as a road traffic accident.
"But we went over the good times - and there were many. In the end, we laughed. Why would you not laugh? Diana was great fun.
"I remember having many conversations with Diana's mother, who didn't have a great deal of time for the Royal Family. She said: 'We're not royal, that's the thing.'
"In a way, Diana was not royal in the sense she was always easier being pally with the shop floor than the management.
"She was ahead of the game in that respect, but the Royal Family weren't prepared to accept it. They do now, and I think they are the better for it."