Prince William releases a statement heavily criticising the BBC's Panorama programme for the deceitful way it obtained an interview with his mother, Princess Diana.
William said the programme increased her “fear, paranoia and isolation” in her final years, and that the show had no legitimacy and should never be shown again.
His brother, Prince Harry, said that "the ripple effect of a culture of exploitation and unethical practices ultimately took her life".
Prince William and Prince Harry were responding to the Dyson report, which found that BBC journalist Martin Bashir used false documents to induce Earl Charles Spencer to introduce him to his sister Diana and set up the Panorama exclusive – "An Interview with HRH the Princess of Wales" – on November 20, 1995.
The BBC set up the investigation, led by former senior judge John Dyson, in November after allegations from Earl Spencer that he had been tricked.
The inquiry found that Bashir used "deceitful behaviour" and was in "serious breach" of the BBC's producer guidelines to secure the interview, which made global headlines.
The BBC has written to the royal family to apologise for the circumstances surrounding the interview.
Prime Minister Boris Johnson said he was concerned by the report's findings.
"I can only imagine the feelings of the, the Royal Family and I hope very much that the BBC will be taking every possible step to make sure that nothing like this ever happens again," he said.
Justice Secretary Robert Buckland said earlier that the BBC's apology to the royal family was "not the end of it".
He confirmed the government would be looking into the broadcaster's "governance and the way it operates".
"We all need to look at this soberly and calmly – the report is damning and no one can get away from that," he told Sky News.
Culture Secretary Oliver Dowden also flagged reforms of the publicly-funded broadcaster.
“Lord Dyson’s report reveals damning failings at the heart of the BBC,” he said on Twitter.
“We will now reflect on Lord Dyson’s thorough report and consider whether further governance reforms at the BBC are needed in the mid-term charter review.”
In the interview, Diana said: “Well, there were three of us in this marriage, so it was a bit crowded.” The reference was to Prince Charles rekindling his relationship with Camilla Parker Bowles, now his second wife.
It was the first time Diana had commented publicly about her doomed marriage.
She died on August 31, 1997, when a car in which she was travelling crashed in the Pont de l'Alma tunnel in Paris as it was being pursued by paparazzi.
“It is my view that the deceitful way the interview was obtained substantially influenced what my mother said," William said.
"The interview was a major contribution to making my parents’ relationship worse and has since hurt countless others.
“It brings indescribable sadness to know that the BBC’s failures contributed significantly to her fear, paranoia and isolation that I remember from those final years with her.
“But what saddens me most is that if the BBC had properly investigated the complaints and concerns first raised in 1995, my mother would have known that she had been deceived.
"She was failed not just by a rogue reporter, but by leaders at the BBC who looked the other way rather than asking the tough questions.
"It is my firm view that this Panorama programme holds no legitimacy and should never be aired again.
"It effectively established a false narrative which, for over a quarter of a century, has been commercialised by the BBC and others.
“In an era of fake news, public-service broadcasting and a free press have never been more important.
"These failings, identified by investigative journalists, not only let my mother down, and my family down, they let the public down too.”
Prince William said the report found BBC employees "lied and used fake documents to obtain the interview with my mother; made lurid and false claims about the royal family which played on her fears and fuelled paranoia; displayed woeful incompetence when investigating complaints and concerns about the programme; and were evasive in their reporting to the media and covered up what they knew from their internal investigation".
Prince Harry said: “Our mother was an incredible woman who dedicated her life to service. She was resilient, brave, and unquestionably honest.
"The ripple effect of a culture of exploitation and unethical practices ultimately took her life.
“To those who have taken some form of accountability, thank you for owning it. That is the first step towards justice and truth.
"Yet what deeply concerns me is that practices like these – and even worse – are still widespread today. Then, and now, it’s bigger than one outlet, one network or one publication.
“Our mother lost her life because of this and nothing has changed. By protecting her legacy, we protect everyone and uphold the dignity with which she lived her life.
"Let’s remember who she was and what she stood for.”
Earl Spencer has said he "draws a line" between the Panorama interview with his sister and her death two years later.
Judge Dyson's report included a handwritten note from Diana from a month after the interview in which she said she had no regrets and that Bashir did not show her any information of which she had not been previously aware.
"By his deceitful behaviour ... Mr Bashir succeeded in engineering the meeting that led to the interview," the report said.
"But it is important to add that Princess Diana would probably have agreed to be interviewed."
After it was broadcast, Bashir repeatedly lied to his bosses about how the interview was obtained, the report said.
As questions continued, BBC managers failed to scrutinise his version of events properly and covered up facts about how he had secured the interview.
An internal investigation by the BBC into the matter in 1996 was “woefully ineffective”, the report found.
The inquiry “did not scrutinise Mr Bashir’s account with the necessary degree of scepticism and caution”, the report said, despite the fact he “had lied three times when he said that he had not shown the fake statements to Earl Spencer”.
It also said Mr Bashir was “unable or unwilling” to offer a credible explanation of why he had commissioned the fake statements and why he had shown them to Earl Spencer, and Earl Spencer was not approached to give his version of what had happened.
Former BBC director general Lord Tony Hall, who led news and current affairs when the Diana interview was screened, has apologised.
"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," Mr Hall said.
In a new Panorama programme broadcast on Thursday, Earl Spencer said: "The irony is that I met Martin Bashir on August 31, 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 that I sat in on September 19, 1995, everyone was going to be made untrustworthy and I think that Diana did lose trust in really key people.
“This is a young girl in her mid-30s who has lived this extraordinarily turbulent and difficult 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.”