Princess Diana Said Her Marriage Was 'Hell' and Prince William Should Be King Instead of Charles

Princess Diana laid bare how her marriage to Prince Charles was "hell from the start" and how she didn’t believe he was fit to be King in a previously-unknown series of revelations.

The princess described her private pain in a chat with a newspaper editor three months before she went on to graphically tell the world of her unhappiness in the BBC Panorama show in 1995.

Now, almost 25 years after that stunning interview when Diana notoriously said, “There were three of us in this marriage . . . so it was a bit crowded,” a new documentary reveals how she had had already sought to tell her story.

In Diana: The Truth Behind the Interview, airing at 9 p.m. on Wednesday in the U.K., former newspaper editor Sir Max Hastings says, “She said I was terribly anxious for my side of this to come out. And I spent as part of a couple of hours with Diana and she put on a wonderful show. I mean, absolutely gripping stuff.”

“It became clear, first of all. How much she hated Charles. Yes, she did hate Charles. And when I said 'were there ever happy times?' she said 'no, the marriage was hell from day one,'” he adds.

RELATED: Princess Diana's Panorama Interview Is Still Shocking 25 Years Later: 'There Were 3 of Us in This Marriage'

Hastings says that Diana had the prospects of her eldest son Prince William in mind.

“She said that all she cared about was William's succession to the throne. She said to me quite explicitly — 'I don't think Charles can do it,'" he says. “The outcome she wanted to see was for Charles to stand aside as heir to the throne and for William to occupy the throne. This was pretty dynamic stuff.”

The former editor of the Daily Telegraph explains that he didn’t publish Diana’s words because he wanted to “keep a lid on the worst of this,” and thought that much of what Diana said “on several occasions” was “for the fairies.”

“She asked me what I knew about a conspiracy to have her put down. I said well, ‘it sounded absolutely crazy to me.’ But she, I think, did believe this sort of stuff," he says in the documentary, adding that he felt “so desperately sorry her” in her “vulnerability.”

The story comes as Netflix’s The Crown prepares to air its fourth season, which lays bare the unhappiness in the royal marriage.

And the new documentary also raises questions about how interviewer Martin Bashir secured the support of Diana’s brother Charles, the 9th Earl Spencer. The documentary echoes claims made recently in The Sunday Times that fake documents were shown to Spencer purporting to show a former member of his staff receiving payments for information. It played on his — and Diana's — fears of being watched or tracked by security services, it was said.

Earlier this month, the BBC told the Sunday Times that Bashir is unwell and unable to respond.

“Questions surrounding Panorama’s interview with the Princess of Wales and in particular the ‘mocking-up’ of bank statements, were covered in the press at the time," the statement reads. "BBC records from the period indicate that Martin had explained to the BBC that the documents had been shown to Earl Spencer, and that they were not shown to the Princess of Wales. The BBC’s internal records from the time indicate that Martin had met the Princess of Wales before the mocked-up documentation existed. These accounts also say that the Princess of Wales confirmed in writing that these documents played no part in her decision to give [the interview].”