Journalist Martin Bashir tricked princess Diana into giving an explosive BBC television interview in which she lifted the lid on her troubled marriage to Prince Charles, an independent investigation concluded on Thursday.
Retired senior judge John Dyson said Bashir commissioned faked bank statements that falsely suggested some of Diana's closest aides were being paid by the security services to keep tabs on her.
Bashir then showed them to Diana's brother Charles Spencer, in a succesful bid to convince him to arrange a meeting between himself and Diana and earn her trust.
Dyson said he was "satisfied" that Bashir showed fake bank statements "so as to deceive Earl Spencer and induce him to arrange the meeting with Princess Diana".
"By behaving as described... Mr Bashir acted inappropriately and in serious breach" of the corporation's own editorial guidelines on "straight dealing", Dyson added.
Questions have long been asked about how Bashir convinced Diana to talk on the BBC's flagship "Panorama" programme in November 1995, which was watched by a record 22.8 million people and won a string of television awards.
In it, she famously said "there were three people" in her marriage -- her, Charles and his long-time mistress and now wife, Camilla Parker-Bowles -- and also admitted adultery.
Bashir, now 58, was little-known at the time of the interview but went on to have a high-profile career on US television networks, and interviewed stars such as Michael Jackson.
He returned to work for the corporation as religion editor until he stepped down last week, citing ill health, just hours before Dyson's report was submitted to BBC bosses.
- 'Flawed and ineffective' -
A 1996 internal inquiry by future BBC chief Tony Hall and another senior figure, Anne Sloman, cleared Bashir of wrong-doing.
But Dyson called that probe "flawed and woefully ineffective".
In particular, it did not ask Diana's brother, Charles Spencer, for his version of events, Dyson said, lambasting it for failing to scrutinise Bashir's actions properly.
"If they had been able to test Mr Bashir's account by asking him to comment on Earl Spencer's detailed account, it is very unlikely that they would have believed him and concluded that he was an 'honest and an honourable man'," he wrote.
Hall, now chair of the board of trustees at Britain's National Gallery, admitted that the probe "fell well short of what was required", and said he was "wrong to give Martin Bashir the benefit of the doubt".
- Full apology -
The Daily Telegraph earlier suggested the report's findings were comparable to phone-hacking revelations at Britain's News of the World tabloid, which forced its closure.
Diana's friend, Simone Simmons, told The Sun that the interview had "destroyed her pyschologically" and "made her paranoid".
BBC director-general Tim Davie said the corporation accepted Dyson's findings completely, and offered a "full and unconditional apology".
The broadcaster also said it was handing back the awards the programme won for the interview.
Bashir also apologised, saying the faking of the bank statements was "a stupid thing do and was an action I deeply regret".
But he maintained it had "no bearing whatsoever on the personal choice by Princess Diana to take part", and he was still "immensely proud" of the interview.
- 'Rogue reporter' -
Davie equally said the princess was "keen on the idea of an interview with the BBC". Her estranged husband had spoken to commercial channel ITV in 1994, and also admitted adultery.
But he added: "It is clear that the process for securing the interview fell far short of what audiences have a right to expect. We are very sorry for this."
"Clear failings" had been identified, he added, but said the BBC now had "significantly better processes and procedures" than at the time.
"The BBC should have made greater effort to get to the bottom of what happened at the time and been more transparent about what it knew," Davie added.
John Birt, director-general of the corporation at the time of the interview, said in a statement: "We now know that the BBC harboured a rogue reporter".
Diana and Charles formally divorced in 1996. She died aged 36 in a high-speed car crash while being chased by paparazzi photographers in Paris the following year. Charles married Camilla in 2005.