The mood on the helicopter heading from London to the landing pad by the Eiffel Tower was somber. Thirty-two hours after the death of Diana, Princess of Wales, I was flying on Mohamed Fayed’s helicopter with three others: his security chief, a Scottish pathologist hired to deliver a verdict approved by Fayed on the condition of the dead chauffeur, and a Washington lawyer. He was tasked to protect Fayed from any personal recrimination for the fatal accident.

Minutes after we landed in Paris we were heading towards the Ritz hotel, the scene of the last sighting of Dodi Fayed and Diana. Mohamed Fayed had personally agreed that I would be allowed to interview all the hotel’s staff who had cared for the couple during their last hours. What I heard from 14 of Fayed’s employees over the next 24 hours was astonishing. Not least because the real story of Diana’s romance over the previous weeks in the South of France with Fayed’s wastrel son Dodi had magnified Fayed’s well-established notoriety in Britain.

Diana leaves Dodi Fayed’s apartment on Rue Arsène-Houssaye with bodyguards Alexander “Kes” Wingfield and Trevor Rees-Jones, on the way to the Ritz on August 31, 1997.

Until then, even Britain’s libel laws had not protected Fayed from accusations that he was a dishonest, tax-dodging, sex-mad blackmailer. He was widely accused of masterminding a defamatory battle to preserve his ownership of Harrods and secure a British passport and, after exposing two sleazy Tory MPs for accepting his cash to ask questions in the Commons, of being corrupt.

The world was littered with his accusers: the Maktoums of Dubai alleged that he defrauded them, honest Harrods staff accused him of contriving false allegations of theft, and even Haiti’s murderous dictator, Papa Doc Duvalier, accused Fayed of deception.

No one was a more bitter enemy than German-born Tiny Rowland, a buccaneering tycoon. Rowland had exposed Fayed’s claim to be the son of a rich Egyptian pasha as untrue. The son of an impoverished school inspector in Alexandria, Fayed had constantly re-invented his own biography – even adding “Al” to his name to suggest a noble birth and reducing his age by three years. He was born in 1929.

Steely willpower, breathless cunning and ruthless exploitation of any individual’s greed or vulnerability was Fayed’s armory to promote his own fortune. And so, in summer 1997, Princess Diana was lured into his web.

After the deaths of the Duke and Duchess of Windsor, Mohamed Fayed acquired their property in the Parisian park Bois du Boulogne and renamed it the “Villa Windsor.”

Frustrated that she could not find anywhere to spend the summer with her sons, William and Harry, Diana snapped up Fayed’s invitation to spend two weeks at his villa in St Tropez. Naïvely, Diana failed to realize that Fayed was plotting to use her to secure his acceptance by the British establishment. “The idea is that you have a quiet, private family holiday,” Diana was told by Michael Cole, Fayed’s spokesman.

What I heard from 14 of Fayed’s employees over the next 24 hours was astonishing.

Amid a blaze of global publicity, Diana spent about three weeks by the Mediterranean – first with her sons and then alone with Dodi Fayed. During those weeks, I regularly visited Fayed at Harrods. My critical biography of his old foe Rowland had won his trust. Each time, Fayed showed me the latest photos of himself with Diana. Or Diana with Dodi. Fayed boasted how he had bought a second yacht for Dodi to seduce Diana – Fayed’s principal yacht was occupied by Dodi’s American fiancée. Anticipating their wedding in three weeks, she was junked, Fayed would tell me.

The mystery, 32 hours after Diana’s death, was how the Princess ended up with Dodi and why she had been driven by a drunken driver, Henri Paul, from the Ritz through Paris. I hoped those questions would be answered as I sat with Fayed’s security chief, John Macnamara, in the Ritz bar. Formerly a chief superintendent at Scotland Yard in charge of the fraud squad, Macnamara had become infamous for fixing false evidence to secure the prosecutions of innocent people, intimidating Fayed’s critics and bribing policemen.

Alongside Macnamara was Alex “Kes” Wingfield, the second of Diana’s bodyguards during the summer, paid by Fayed. Wingfield had not been in the doomed Mercedes. “Henri Paul,” Wingfield told me at Macnamara’s behest, “had sat in the bar with me drinking cordials before he set off with Dodi and Diana.” Unexpectedly, I became suspicious. I had not asked Wingfield if the Mercedes’ dead driver was drunk. (The autopsy’s result was released later that day.) Eager not to ruin my interviews with the eyewitnesses to Diana’s last hours, I nodded. Later, the Ritz barman told me that Paul had drunk two Ricard pastises.

Diana and Dodi (both partially visible in the back seat), with Rees-Jones and chauffeur Henri Paul, who was later found to have a blood-alcohol level three and a half times over the legal driving limit, in their Mercedes-Benz S280.

My interviews were conducted in a paneled boardroom. In succession, the Ritz’s waiters, housekeepers, security staff and Claude Roulet, the deputy manager, were ferried into the room by Macnamara. Their accounts described how Diana calmly watched Dodi, agitated by the paparazzi outside the Ritz, discuss on the telephone from the Imperial Suite an escape ruse through the rear entrance with his father.

Kes Wingfield and Trevor Rees-Jones, the second bodyguard, they agreed, had opposed the plan to return for the night to the Fayeds’ apartment block on the Champs-Élysées. Roulet was witness to Fayed’s micro-management. “It’s been okayed with Mr Mohamed,” he heard Henri Paul tell the bodyguards. Dodi, the bodyguards knew, did nothing without his father’s approval. Quite clearly, Fayed had authorized the high-speed chase which Paul started at 12.25am and ended in an underpass tunnel. But the totality of Fayed’s control only emerged hours later.

At the end of the interviews, Macnamara angrily entered the room. He had not liked the interviews, he said. To my surprise, he had been listening through a concealed microphone. Now I understood an undertone during those interviews. Bugs and video cameras were installed in many of the Ritz’s rooms. Guests’ telephone calls were routinely recorded. And Fayed employed armed bodyguards because he feared assassination. Macnamara ran Fayed’s reign of terror.

“You can’t stay the night here,” announced Macnamara. “You can either go back to London at your own expense or stay the night in Mohamed’s flat.” I chose the latter, unaware that Macnamara had handed me an extraordinary opportunity.

With its shattered windshield, deflated airbags, and broken engine, the car was barely recognizable after the crash.

The flat was Diana’s destination in the race from the Ritz. The dark building’s only occupant was Rene Delorm, Dodi’s long-serving valet. Delorm had been a unique witness to the love affair over the previous weeks. Distraught, he nevertheless described to me through the night the intimacy of the Fayeds’ seduction of Diana — both Mohamed’s and Dodi’s. By daylight I had a reliable impression of the couple’s intimacy on the yacht, Diana’s tolerance of Dodi’s ingestion of drugs and her undoubted affection for Dodi.

Revealingly, Delorm confirmed that Dodi’s seduction of Diana had been choreographed by his father. It had started during a short “innocent” evening in Paris, followed by ferrying Diana on Mohamed Fayed’s private jet to Nice. Once on the yacht, Fayed anticipated, Diana would become Dodi’s lover and eventually, Mohamed hoped, his wife.

After hearing about his son’s conquest, Fayed arranged for a photographer to snap the couple in Sardinia. On Fayed’s initiative, a newspaper described Diana being involved in her “first serious romance” since her divorce. Then, the floodgates opened. Daily, with Fayed’s encouragement, the world’s media recorded the affair. Convinced that he had entrapped the world’s most famous icon, Mohamed Fayed imagined in due course joining the royal family through marriage. The crash shattered his plot.

Bugs and video cameras were installed in many of the Ritz’s rooms. Guests’ telephone calls were routinely recorded.

What followed was a coward’s revenge on fate. At first, Fayed spoke through Michael Cole about the couple being hounded to death by ruthless paparazzi. Then his story unraveled. Henri Paul, the autopsy showed, was not only drunk – he had consumed the equivalent of 11 shots of whiskey – but he had also challenged the paparazzi outside the Ritz: “Don’t bother following – you won’t catch us.”

According to reports, the car carrying Dodi and Diana was traveling at about 70 m.p.h. in a 30-m.p.h. zone when it crashed in the Pont de l’Alma tunnel.

To protect himself, Fayed spread a succession of malicious lies. At her death, he claimed, Diana was pregnant and had agreed to marry Dodi. They would live in the Villa Windsor in Paris, which he owned. To prevent a Muslim joining the royal family, Fayed claimed, Prince Philip and MI6 had conspired to cause the fatal crash using laser beams and a white Fiat Uno.

My interviews at the Ritz had proved all that to be untrue. The couple’s stopover in Paris was a last-minute decision, and no one other than Fayed and Henri Paul knew the Mercedes’ route from the Ritz to the Champs-Élysées. Finally, all the eyewitnesses at the Ritz agreed that the Repossi ring Dodi gave to Diana that afternoon was not an engagement ring but a token of friendship. Marriage, Delorm confirmed, had not been discussed.

The conspiracy stories were fueled by Fayed’s employees — Macnamara and Cole — and reckless TV stations and newspapers. But most of all by Fayed himself. With animal-like passion, he was furious that his lies were not accepted as the truth.

Inexplicably, Fayed’s false conspiracy theories about the crash were officially crushed only ten years after Diana’s death. Unable to produce a scintilla of evidence of a conspiracy at the inquest, Fayed heard a judge conclude that Diana was killed as a result of a drunken driver racing too fast, and her failure to wear a safety belt.

Shamelessly, Fayed left the court without a word of apology for defaming the royal family and Diana’s memory. Twenty-five years later, it’s time to silence his self-serving fantasies.

Tom Bower is a London-based investigative journalist and broadcaster. He is the author of 25 books, including Revenge: Meghan, Harry and the War Between the Windsors