LONDON, England (AP) — A BBC journalist used “deceitful behaviour” to secure an explosive interview with Princess Diana in 1995, in a “serious breach” of the broadcaster’s guidelines, an investigation found Thursday.

The BBC said in November it had appointed a retired senior judge to lead an investigation after Diana’s brother, Charles Spencer, made renewed complaints that journalist Martin Bashir used false documents and other dishonest tactics to persuade Diana to agree to the interview.

Spencer alleged Bashir showed him fake bank documents relating to his sister’s former private secretary and another former royal household member, with the aim of gaining access to the princess.

The interview, in which Diana famously said “there were three of us in this marriage” — referring to Prince Charles’ relationship with Camilla Parker-Bowles — was watched by millions of people and sent shockwaves through the monarchy.

The BBC’s chairman, Richard Sharp, said the corporation accepts the investigation’s findings, adding “there were unacceptable failures.”

John Birt, director-general of the BBC at the time of the interview, which was aired on the “Panorama” news program, apologised to Charles Spencer in a statement.

“We now know that the BBC harboured a rogue reporter on Panorama who fabricated an elaborate, detailed but wholly false account of his dealings with Earl Spencer and Princess Diana,” he said. “This is a shocking blot on the BBC’s enduring commitment to honest journalism; and it is a matter of the greatest regret that it has taken 25 years for the full truth to emerge.”

The investigation considered whether actions taken by Bashir influenced Diana’s decision to give the interview. It also looked into how much the BBC knew about the “mocked-up bank statements” that Charles Spencer claimed Bashir produced.

Diana divorced from Charles in 1996 and died in a Paris car crash in 1997 as she was pursued by paparazzi. Charles married Camilla, now the Duchess of Cornwall, in 2005.

Bashir, who was the BBC News religion editor, left the corporation last week on health grounds. He has been seriously unwell with COVID-19-related complications.