Princess Diana began self-harming just three months into her marriage to Prince Charles.

As they waved to the crowds on their wedding day, Prince Charles and Princess Diana looked the picture of happiness. With hindsight, we know the reality was anything but.

Various sources have offered insight into Diana’s thoughts on the matter, including author Andrew Morton’s biography Diana: Her True Story (revealed later to have been written with her cooperation) which shocked when it was first published in 1992, and again when it was republished after her death in 1997 with further information from the pair’s exchanges.

Now in an extract from the updated version marking the book’s 25th anniversary, full transcripts of Princess Diana’s tapes reveal even more detail – and paint an even bleaker picture.

"We got married on Wednesday. On the Monday (July 27, 1981), we had gone to St Paul's for our last rehearsal, and that's when the camera lights were on full and I got a sense of what the day was going to be," reads an extract published by the Daily Mail.

"And I sobbed my eyes out. I absolutely collapsed and it was because of all sorts of things. The Camilla thing rearing its head the whole way through our engagement.

"I was desperately trying to be mature about the situation, but I didn't have the foundations to do it, and I couldn't talk to anyone about it."

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The ceremony and honeymoon didn't get any better, with Diana quickly realising the reality of what she'd gotten into.

"I thought, you know, it was just grim. I just had tremendous hope in me, which was slashed by day two," she allegedly said.

Her battle with bulimia worsened reaching "appalling" levels by the second leg of the honeymoon, with the newlywed often being sick four times a day.

"So, of course, that slightly got the mood swings going, in the sense that one minute one would be happy, the next, blubbing one's eyes out," she recounted. (Post continues after gallery.)

"I remember crying my eyes out on our honeymoon. I was so tired, for all the wrong reasons totally."

Haunted by thoughts and fears of Camilla and an inattentive husband, Diana got thinner and sicker.

Three months after the wedding while the pair were staying at Balmoral in Scotland, she was in a "very bad way", "so depressed" she starting trying to self-harm.

She returned to London to seek treatment, where she said "all the analysts and psychiatrists you could ever dream of" tried to sort her out.

"But the Diana that was still very much there had decided just time, patience and adapting were all that were needed. It was me telling them what I needed," she said.

"They were telling me 'pills'! That was going to keep them happy — they could go to bed at night and sleep, knowing the Princess of Wales wasn't going to stab anyone."

Finding out she was pregnant with William soon after was a "godsend" that lifted things for a while but it was short-lived.

Constantly feeling she wasn't good enough, wearing the "wrong clothes, wrong everything" and with little sympathy from her husband and family, Diana struggled.

"I couldn't sleep, didn't eat, whole world was collapsing around me. Very, very difficult pregnancy indeed. Sick the whole time, bulimia and morning sickness," she said.

"With William, it was appalling: almost every time I stood up, I was sick.

"I couldn't define what triggered it off, but obviously I felt it was a nuisance to the set-up — and I was made to feel it was a nuisance to the set-up."

If you or a loved one is suffering with an eating disorder, Mamamia urges you to contact The Butterfly Foundation here. You can call Butterfly's National Helpline on 1800 334 673 or e-mail support@thebutterflyfoundation.org.au