Martin Bashir and his film crew sneaked into Kensington Palace to interview Princess Diana by disguising themselves as tradesman.
The shocking revelation has come to light for the first time after a damning report found the journalist faked bank statements to dupe Diana into agreeing to the interview.
The disguise was revealed during a BBC Panorama special on Thursday which explained how Martin and his team "slipped into the palace" dressed as workmen on November 5, 1995 to conduct the bombshell interview.
Lord Dyson, a former master of the rolls and head of civil justice, was appointed to look into the interview which was watched by an estimated 2.5 billion people worldwide.
His inquiry found Bashir used “deceitful behaviour” in “serious breach” of the BBC’s guidelines to secure the interview.
Bashir’s shocking tactics included showing faked bank statements to Diana’s brother Earl Spencer in a bid to falsely suggest a number of close aides were being paid to leak secrets.
Earl Spencer believed Bashir’s claims aimed to heighten Diana’s paranoia about who she could trust – thus making her keen to tell her side of the story in a TV interview with him.
Speaking on the Panorama special, he said: "The irony is I met Martin Bashir on the 31st August 1995 because exactly two years later she died and I do draw a line between the two events.
"It's quite clear from the introduction I sat in on on the 19th September 1995 everybody was going to be made untrustworthy and I think Diana did lose trust in really key people.
"This is a young girl in her mid 30s who has lived this extraordinarily difficult and turbulent time in the public eye - she didn't know who to trust - and in the end when she died two years later, she was without any form of real protection."
Bashir has apologised saying he 'deeply regretted' faking the bank statements.
But he added: “The bank statements had no bearing whatsoever on the personal choice by Princess Diana to take part in the interview.
“Evidence handed to the inquiry in her own handwriting unequivocally confirms this.”
A 1995 letter from Diana – published as evidence – said she had “no regrets”.
She wrote: “Martin Bashir did not show me any documents, nor give me any information that I was not previously aware of."
Earl Spencer has pointed the finger at Bashir over Diana's tragic death on the expose.
He said Diana was "vulnerable" and after the interview she was left with no protection when she was killed in a car crash in Paris in 1997.
The BBC will be stripped of awards for the Panorama interview
Former BBC director-general Lord Hall, who investigated Mr Bashir in 1996 after questions were first raised, said he accepts the original inquiry into the interview "fell well short of what was required".
He added: "I have read Lord Dyson's report, and I accept that our investigation 25 years ago into how Panorama secured the interview with Princess Diana fell well short of what was required. In hindsight, there were further steps we could and should have taken following complaints about Martin Bashir's conduct.
"I was wrong to give Martin Bashir the benefit of the doubt, basing that judgement as I did on what appeared to be deep remorse on his part. Throughout my 35-year career at the BBC, I have always acted in ways I believe were fair, impartial and with the public interest front and centre.
"While Lord Dyson does not criticise my integrity, I am sorry that our investigation failed to meet the standards that were required."
Former BBC governor Sir Richard Eyre said the board of governors would have insisted on a full inquiry had they known the truth about Bashir’s actions.
The Panorama interview was broadcast a year before Diana and Prince Charles were formally divorced in 1996, though they had separated in 1992.
In the sensational recording in November 1995 Diana admitted committing adultery and being in love with James Hewitt.
She also uttered the now infamous line “there were three of us in the marriage, so it was a bit crowded” in relation to Charle’s affair with his now wife Camilla.
