A Balmoral attendant has revealed the moment Charles and Diana's marriage started to 'deteriorate' while at the Scottish estate, not long after their 1981 wedding.

The claims are made by an unnamed gilly (a hunting and fishing expert) in royal author Tom Quinn's new book Yes, Ma'am: The Secret Life of Royal Servants, which is to be released next month.

In an extract from the book, seen by FEMAIL, which details accounts from royal servants over the years, the guide shared how the late Princess of Wales hated Balmoral.

Speaking anonymously, the attendant explained that Diana's hatred of the Scottish residence came from her boredom with the traditional outdoor pursuits - despite growing up in nature and coming from a family who enjoyed hunting and fishing.

He added that she preferred the city and disliked country sports - an admission that completely shocked the then Prince of Wales, who was a keen fox hunter.

King Charles adored stalking as a young man and after his first kill was apparently smeared with the blood of the first fox and the first stag he shot and killed as per royal tradition.

But Diana was less impressed and couldn't throw herself in to the activity and it was that - not her husband's infidelity - that is said to have undermined their marriage from the start.

The insider said: 'That, I think, was the start of the deterioration of their relationship, whatever people say about it being entirely about the other woman!'

Meanwhile, Diana's boredom led to some cheeky jokes to pass the time, according to the book. 

During one outing as she accompanied her husband on one of his favourite pursuits, she let her boredom get the better of her and teased the group of enthusiastic fishers, the guide claimed.

The gilly recalled: ‘I remember once she was sitting quietly watching all the casting and discussions about which flies to use. 

'She looked a little bored and when everything fell quiet for a moment she called across to Prince Charles, “Darling, wouldn’t it be easier to just use a net!”.’

The then Prince and Princess of Wales' different hobbies apparently became a constant point of contention throughout their marriage. 

In nine letters written by Princess Diana in the early years of her doomed marriage to Charles, which were auctioned off in June, she told Maud Pendrey, her family's former housekeeper, how her honeymoon was a 'tremendous success' and said she and Charles had a 'glorious time'.

But her letters hid a sad truth and Penny Junor, author of The Duchess, wrote that the couple's differences became quite stark on their honeymoon. 

Whilst the future King envisioned swimming, reading, painting, and writing thank-you letters, Diana had expected to chat.

'He'd taken along his watercolours, some canvases and a pile of books by the Afrikaner mystic and writer Laurens van der Post, which he'd hoped he and Diana might share and then discuss in the evenings,' Ms Junor wrote.

'Diana, however, was no great reader. She hated his wretched books and was offended that he might prefer to bury his head in one of them rather than sit and talk to her. She resented him sitting for hours at his easel, too, and they had many blazing rows.

'One day, when Charles was painting on the veranda deck of Britannia, he went off to look at something for half an hour. He came back to find she'd destroyed his painting and all his materials.'

In 2018 a bombshell royal biography by royal reporter Robert Jobson revealed Prince Charles agonised over his decision to call off his wedding to Diana. 

Despite realising that he and the aristocrat's daughter were incompatible, he felt powerless to do anything about it. Breaking off the engagement 'would have been cataclysmic', he said.

Years later and still troubled by the tragedy of the marriage, he wept tears of frustration as he told friends: 'I desperately wanted to get out of the wedding in 1981, when during the engagement I discovered just how awful the prospects were.'

Other bombshells revealed in Tom Quinn's latest book include the extent of King Charles' temper.

The biography reveals the king will 'lose his temper in a split second' if his very particular demands aren't fulfilled, insiders have claimed in an upcoming book.

Insiders explained that Charles and Queen Camilla always treat their staff 'well', but that the King is prone to 'little bursts of irritation'.

Charles, who is widely known to have a temper and has previously fumed in public over his pens not working, has very particular demands for how tasks are carried out.

The monarch was said to have kicked up a fuss if he wasn't given the 'right teacup' and also had opinions on how his toothpaste was placed on his brush.

In an extract from Yes Ma’am: The Secret Life of Royal Servants seen by FEMAIL, one servant recalled: 'Charles and Camilla do treat their staff well, but you always feel that they would no more fly without an aeroplane than invite you to have tea with them.

'And Charles does have little bursts of irritation with his staff – perhaps he hasn’t been given exactly the right teacup, perfectly polished shoes and toothpaste neatly squeezed on to his toothbrush in exactly the way he likes it.

'He loses his temper in a split second but usually quickly regrets it.' 

Yes, Ma'am: The Secret Life of Royal Servants by Tom Quinn (published by Biteback, £20) is available for pre-order.