According to a new report, Prince Charles was questioned by British police in 2005 about the death of his ex-wife, Princess Diana.

On Monday, former Scotland Yard chief John Stevens told the U.K.’s DailyMail that he needed to “follow the evidence” and interview the Prince of Wales about a letter Diana wrote alleging he was plotting a vehicle accident.

The Metropolitan Police inquiry was focused on an accusation of plot to kill the couple made by Mohamed Al-Fayed, whose son, Dodi Al-Fayed, died in the same automobile accident as Diana in August 1997. The investigation’s results, which were broadcast by the BBC in 2006, indicated that their killings were not premeditated.

According to the Daily Mail, the inquiry was part of “Operation Paget,” which was started by the British Metropolitan Police in 2004 to look into conspiracy theories surrounding Diana’s demise.

Stevens said that he discussed with Prince Charles a letter written by Princess Diana in 1995 that stated, “My husband is planning ‘an accident’ in my car, brake failure and serious head injury,” in order for him to marry Tiggy Legge-Bourke, a nanny for Prince William and Prince Harry.

“This particular phase in my life is the most dangerous — my husband is planning ‘an accident’ in my car,” Diana allegedly said in the note acquired by the Daily Mail.

“Camilla is nothing but a decoy so we are being used by the man in every sense of the word.”

A year later, in 1996, the couple divorced.

According to the source, Charles, now 72, was questioned as a witness at St. James’s Palace two years after the letter was made public in 2003.

“Yes, allegations had been made about the Prince of Wales and other royals but we had to find or examine the [existing] evidence before we approached him with formal questions,” Stevens said. “We found no other evidence to support the scenario suggested in Diana’s note.”

“We were left with the note, which in itself was not enough to make Charles a formal suspect,” Stevens continued. “If he chose to assist [Operation] Paget, he would be doing so voluntarily as a potential witness. We would not be interviewing him under caution.”

According to reports, Stevens read the note to Prince Charles and then asked him, “Why do you think the princess wrote this note, sir?”

“I did not know anything about [the note] until it was published in the media.” the prince said.

“You didn’t discuss this note with her, sir?” Stevens inquired, to which Charles replied, “No, I did not know it existed.”

“Do you know why the princess had these feelings, sir?” he asked. “No, I don’t.” Charles answered.

“At the end of the day,” Stevens told the Daily Mail, “he was incredibly cooperative because he had nothing to hide.”

Prince Philip, Charles’ father, refused to help in the probe. When asked to respond on the accusations, the Duke of Edinburgh simply said, “No, thank you.”

According to The Independent, Burrell revealed in his 2003 book, “A Royal Duty.” that Diana sent him the note. Burrell handed the original letter to police for the inquiry and “did not know what had prompted Diana to write the note.”

The letter was sent around the time the Princess interviewed Martin Bashir, who was recently discovered to have engaged in “deceptive behavior” by creating false financial statements to obtain her interview with the former BBC journalist. Stevens acknowledged that he and his colleagues “regretted” not interviewing Bashir at the time.

An investigation led by former Supreme Court Justice John Dyson concluded last month that Bashir used “deceitful methods” to obtain the interview.

Stevens expressed sorrow that he and his colleagues did not conduct an interview with Bashir.

“If there’d been an allegation then that Bashir had produced allegedly fake documents to Princess Diana, which is a criminal offense, we’d have investigated it. My goodness me, we would have done,” he said. “But this has only come out recently, which is unfortunate.”