The tapes disappeared from Diana's apartment at Kensington Palace after her death in 1997 but were discovered four years ago in the loft of her former butler, Paul Burrell.
Settelen fought a bitter legal battle against Diana's family for ownership of the tapes, which were finally handed back to him in September this year.
In an interview to accompany the tapes, Settelen says Diana came across as a "frightened woman" who was "shellshocked by a bad marriage".
The cameraman, who wishes to remain anonymous, claims he worked for the BBC and was summoned to Kensington Palace late one night.
The Sun reports how the cinematographer kept a diary of the sessions in which he wrote: "Diana caught Charles and Camilla de flagrante after listening in to his phone calls.
"She described how she came to listen to their phone calls. In one, Charles was sitting on the toilet seat when she caught him."
The topic of conversation was described as "phone sex" where it was claimed Camilla was the more saucier of the two.
Diana also spoke about her desire to stop Charles from becoming King, instead wanting her eldest son William to take up the position.
The Sun reported the technician wrote: "She makes it clear that she would do everything possible to make sure Charles never became King.
"She wanted William to succeed to the throne when the Queen died. Diana clearly saw her role as the power behind William.
"She had this somewhat romantic idea of being a king-maker, the mother behind the monarch."
The secret lensman who is still alive and understood to be living in America described the moment he arrived at Kensington Palace and was waved through by police.
He said he was paid £5,000 for the sessions and had to buy two burner phones amid fears Mi5 would hack their conversations.
Overnight the controversial recordings, documenting the collapse of Diana's marriage to Charles, will be aired on Channel 4.
The tapes went missing and Settelen became locked in a copyright battle with Diana's brother, following her death, for the rights to broadcast them.
He eventually won and was backed by NBC who wanted to broadcast the footage.
Settelen was hired by the princess to build her confidence in public speaking but in the process recorded her no-holds-barred confessions about the royals.
This isn't the first time details about Prince Charles' private contact with his now-wife have come to the fore.
In 1992, a highly personal transcript of the "Camillagate" call was made public.
It caused huge embarrassment to the Royal Family as it included details of how the prince had told his lover that he wanted to be her "tampon".
Minutes from a security meeting describing the inquiry into the Camillagate scandal were read to the London hearing into the death of Princess Diana and her lover Dodi Fayed in 2008.
Lord Fellowes, who was then the Queen's private secretary, told the gathering in April 1993: "Evidence had been found that the fixed telephone lines had been tampered with.
"It was almost certain that this was the location where the Prince of Wales had been staying on the night of the alleged conversation between him and Mrs Parker Bowles."
The location was not named, but it is thought to be Eaton Hall in Cheshire, home of Charles's great friend, the Duke of Westminster.
The prince is thought to have enjoyed clandestine meetings with Camilla at the house.
The inquest heard that Charles made the call to Camilla, who was at her home in Wiltshire, on a mobile phone, not a landline.
But the minutes from the meeting showed that Sir Robin Butler, the then Cabinet Secretary, was so concerned about the tampering that he asked whether all royal premises should be checked for listening devices.
The latest revelations emerged as Sir John Adye, the head of GCHQ from 1989 to 1996, gave evidence.
He dismissed claims that the service was bugging the royals and said it was 'nonsense' to suggest that they were behind the Camillagate and Squidgygate tapes.
Under the law GCHQ would have needed to get the Foreign Secretary to sign off such a phone tap, which the agency had not sought, he said.
Ian Burnett QC, for the coroner, said: "And intercepting the Royal Family is simply not within the scope of the intelligence the government was seeking?"
Sir John replied: "Indeed, it was not."
