Lord Stevens reportedly said police launched an investigation after a note Diana wrote in which she predicted she would die in a car accident was discovered.
The police chief told the Daily Mail he needed to question Charles about Diana’s claim that she would be killed because of “brake failure and a serious head injury” so Charles could marry Tiggy Legge-Bourke, William and Harry’s former nanny.
Diana also said Camilla was just a ‘decoy so we’re used by man in every sense of the word’, which was left at Kensington Palace for her butler Paul Burrell.
Charles was questioned as a witness, not a suspect, on December 6, 2005, as part of a three-year investigation. The Prince of Wales said he did not know why Diana wrote the letter, it is reported.
Lord Stevens also told the Daily Mail that police have spoken to former BBC reporter Martin Bashir about the suggestion that he may have made her more paranoid by exploiting her insecurity.
Bashir was found to have used false bank details to trick Diana into giving an interview to Panorama in November 1995.
“If there had been an allegation that Bashir produced false documents to Princess Diana, which is a criminal offense, we would have investigated,” Lord Stevens told the Daily Mail.
“My God, we would have. But it only came out recently, which is unfortunate.
He added: “We don’t know what Bashir was saying to Diana, but if he had put in his mind the fears that led her to write this note, this is what prompted us to interview Charles. When we watched Panorama’s interview at the start of the investigation, it didn’t occur to us that Bashir could have done anything fraudulent.
Diana died with her boyfriend Dodi Al Fayed and their driver Henri Paul when their Mercedes crashed in a Paris tunnel.
In April 2008, a narrative verdict of “unlawful murder [due to the] grossly negligent driving of the following vehicles and the Mercedes ”was returned by an investigation which clarified that Paul was drinking and driving and that he was not wearing a seat belt.