King Charles reportedly blamed his former private secretary for his affair confession in 1994.
At the time, Charles and Princess Diana were still married but had been separated for two years.
Valentine Low, author of a new royal book, said it put an end to the private secretary's career.
King Charles once said it was his former private secretary's idea for him to publicly admit to being unfaithful to Princess Diana in a TV interview, according to a new book.
In 1994, Charles, then known as the Prince of Wales, accepted an invitation to be interviewed on national television by British broadcaster Jonathan Dimbleby. At the time, he and Princess Diana - who he'd married in 1981 - had been separated for two years. It was during that interview that rumors circulating about the nature of his relationship with his now-wife, Camilla, the Queen Consort, were addressed.
Valentine Low, author of "Courtiers: The Hidden Power Behind the Crown" released on Thursday, wrote that the confession caused Charles "untold reputational damage." Low added that it would also be the basis for his private secretary, Richard Aylard, to eventually leave his position in 1997.
Richard Aylard declined Insider's request for comment. Buckingham Palace did not immediately respond to Insider's request for comment.
As Insider previously reported, Charles told Dimbebly during the interview that he was "faithful and honorable" to Diana during their marriage "until it became irretrievably broken down, us both having tried."
Backlash against Charles' confession came not only from the public, but from those close to the royal family, according to Low. In his new book, the author resurfaced an account previously shared in Sally Bedell Smith's 2017 book, "Prince Charles: The Passions and Paradoxes of an Improbable Life," when Charles was asked during a dinner months after the interview about what drove him to confess.
"'He pointed across the table at his private secretary and angrily said, 'He made me do it!'" recalled another dinner guest. 'It was a very unattractive moment,'" the anecdote of one dinner guest went, according to Low.
"For Richard Aylard, it would spell the beginning of the end of his career in royal service," Low wrote. Aylard, he wrote, had previously been brought on to help Diana adjust to her role in the public eye and had been tasked with the responsibility of bridging the ever-widening gap between the princess and Charles as their marriage deteriorated.
"Charles's confession of adultery - confirmed the following day by Aylard at a press conference, at which he spelled out that Charles had been talking about Mrs Parker Bowles - would cause the prince untold reputational damage," Low wrote.
From Aylard's view, it was the right move to convince Charles to "admit adultery," the author added.
"Charles could lie, tell the truth, or evade the question. If he lied, he would certainly be caught out at some point in the future. If he evaded the question, the tabloids would keep digging until they found the evidence they sought," Low went on.
But no matter the logic in Aylard's reasoning, Low wrote that it was pointless - his "days were numbered" under Charles' service because Camilla didn't like him. Although he didn't leave his role until 1997, Low wrote that Aylard's replacement, Mark Bolland, had already been hired and, on multiple accounts, been given the task of getting "rid" of him.
According to an unnamed source interviewed by Low, Charles' confession was the final straw in her first marriage to Andrew Parker Bowles, who she filed a divorce from in January 2005.
"She was really quite cross about the Dimbleby exercise, because that's what really ended her marriage. Camilla had quite a beef with Richard," the individual told Low.