Following a fairytale wedding at St Paul's Cathedral in July 1981, Prince Charles and Lady Diana Spencer were hailed as the royal couple of the century.

But behind the facade of gleaming smiles, by 1982, the 21-year-old princess was in the grips of a painful struggle with bulimia, while also suffering from acute anxiety, low self-esteem and post-natal depression.  

After the birth of her first son, Prince William, in June of that year, Diana made noticeably less public appearances as public concern for her welfare grew.

Indicative of her spiralling mental state, writing in Charles' authorised biography, The Prince of Wales, royal biographer Jonathan Dimbleby detailed the princess's numerous heartbreaking 'suicide bids'.

These included instances of 'throwing herself against glass cabinets', 'cutting her wrists' and even at one stage during her pregnancy, 'throwing herself down the stairs' in front of the late Queen Elizabeth II. 

Such devastating incidents were described as desperate 'cries for help' by the princess's friends and disclosed to journalist Andrew Morton. 

It has been 33 years since Diana and now-King Charles' marriage officially collapsed - with then Prime Minister John Major announcing in Parliament that the pair were to separate in December 1992.

But even 10 years prior, Diana's bitter unhappiness and presumed post-natal depression was beginning to be noticed by the princess's staff who 'made allowances for her erratic and arbitrary behaviour and did their best to adopt to her waywardness'.

Yet only those in Diana's closest circle truly knew the depths of her despair. 

According to Mr Dimbleby, 'one or two' were aware of the princess's tendency to 'consume large quantities of junk food', while others became increasingly concerned about Diana's unwavering suspicion about Charles' 'persistent infidelity'. 

Speaking to Mr Morton in a recorded audio tape in 1991, Diana detailed a terrifying instance in which she had 'thrown herself down the stairs' while four months pregnant with William at Sandringham in early 1982.

The princess revealed: 'We had a few trying-to-cut-wrists, throwing things out of windows, breaking glass. I gave everybody a fright. It was all a desperate cry for help.'

Explaining that the 'suicide bids' had been a desperate attempt at 'trying to get my husband's attention,' Diana emotionally shared: 'I threw myself down the stairs. 

'The Queen comes out, absolutely horrified, shaking - she was so frightened. I knew I wasn’t going to lose the baby, though I was quite bruised around the stomach.

'Charles had gone out riding and when he came back, you know, it was just dismissal, total dismissal. He just carried on out of the door.'

The princess also shared how in June 1986 her older sister, Jane Fellowes, Baroness Fellowes, had come to 'check on me'.

Diana disclosed: 'I had a V-neck on, and shorts. She said: "Duch [Diana’s childhood nickname], what’s that marking on your chest?"

'I said: "Oh, it’s nothing." She said: "What is it?"

'The night before, I’d wanted to talk to Charles about something. He wouldn’t listen to me — he said I was crying wolf.

'So I picked up his penknife off his dressing table and scratched myself heavily down my chest and both thighs. There was a lot of blood — and he hadn’t made any reaction whatsoever.'

At the time, Diana revealed how her sister, four years older than her, had 'went for me,' and told the princess: "You mustn't let the side down."'

In response, Diana was said to have quipped: "Give me some credit that I haven't troubled any of the family in five years about this."'

'Their perception is very different now. They’re annoyed by the lack of support from my husband,' Diana said.

Several of those closest to the princess had been 'led to believe' that Diana's 'alarming behaviour' had been partly 'caused by her husband’s alleged indifference towards her, and specifically by his presumed infidelity with Camilla Parker Bowles,' Mr Dimbleby wrote.

And in the aftermath of such awful events, her friends allegedly reported that Charles had '"scorned her" in the belief that she was "faking her problems."' 

'Burdened by the workload of his own official life, lacking the emotional support at home to which, in this romantic fashion, he had for so long aspired, and drained by the persistence of his wife’s reproaches, he did sometimes rebuff her,' Mr Dimbleby acknowledged.

Yet Charles would, he added, often attempt to 'console' his wife, 'even when, as often happened, she rejected his efforts'.

'It was clear to his friends in whom he confided his bewilderment that he felt tenderness and pity for his wife when she was stricken by these apparently inexplicable moods,' said Mr Dimbleby. 

Eventually, the prince knew he would need to intervene. By the summer of 1982, he had arranged for her to have a session with a psychiatrist. 

While initially little was known of the details of Diana's treatment, in 2017, it was revealed by The Mail on Sunday that the Queen's former physician, Sir John Batten, who treated Diana in the early years of her marriage, believed the princess was suffering from an obscure mental disorder that risked 'dynamic disaster'.

Sir Batten held the belief that the 'dangerous’ condition was genetic and might be passed to her children, while another royal Household doctor and two senior medical figures were said to have shared his startling concerns.

Their views were detailed in an extraordinary letter written in February 1983 by prominent psychotherapist Dr Alan McGlashan, who was brought in to treat the Princess after she allegedly ‘distanced herself’ from the Royal medics. 

According to royal expert Sally Bedell Smith, author of Charles: The Misunderstood Prince, Charles was at 'his wits end' and eventually, out of desperation, invited South-African born philosopher Laurens van der Post to Balmoral to assist.

'He tried soothing Diana, but felt powerless to contain her emotional storms, which shocked him in their intensity and suddenness,' Ms Bedell Smith previously told the Daily Mail.

Diana was said to have been prescribed Valium, however, according to Ms Bedell Smith, 'refused to take it', having been 'convinced in her growing paranoia that The Royal Family was trying to sedate her'. 

While the princess later agreed to have weekly therapy sessions with Dr McGlashan at Kensington Palace, she only saw him eight times.

Instead, it was Charles, described as 'distressed and bewildered', who began having regular therapy with Dr McGlashan, and continued seeing him for the next 14 years.

Since Diana's tragic death in August 1997, her sons, Prince William and Prince Harry, have continued in her efforts to speak openly about mental health issues.

When asked in the 2017 Channel 4 documentary Wasting Away: The Truth About Anorexia whether he was proud of his mother for speaking so openly about her struggles, the future King was clear in his response. 

'Absolutely. These are illnesses. Mental health needs to be taken as seriously as physical health.'

For confidential support call the Samaritans on 116123 or visit a local Samaritans branch, see www.samaritans.org for details.