The pathologist, who reviewed the post-mortem and gave evidence at the official inquiry, said her death was tragically preventable. “If only she had worn a seatbelt, she would have walked out,” he explained. “She may have had a broken rib or a broken arm, but she would have survived. It’s a bad crash, yes, but not catastrophic — and Mercedes are built to take impacts like that. How tragic is it that one simple click could have saved her?”

Only Rees-Jones, the sole survivor, had his seatbelt on, though he still sustained severe facial injuries from hitting the dashboard. Diana’s decision not to buckle up, Dr. Shepherd stresses, made all the difference.

In the years since, conspiracy theories have swirled around Diana’s death, many claiming royal involvement. Dr. Shepherd dismisses them outright. “Well, I’d just shrug my shoulders and say, you’re wrong,” he said. “You can always take 20 facts and weave them into some sort of story. But the reality is simple: Henri Paul was drunk, he was not a skilled driver, he was speeding to outrun the paparazzi. Combine that with no seatbelts, and it was never going to end well.”

An official Metropolitan Police investigation eventually ruled the crash an unlawful killing, citing Paul’s intoxication and the relentless pursuit by photographers.

For Dr. Shepherd, though, the tragedy boils down to one heartbreaking truth: Princess Diana’s life could have been spared with nothing more than a seatbelt.