Watch: Princess Diana's Incredible Legacy Remembered
Diana was "not fully aware of the machine she was in" when she married Prince Charles, according to one of her friends.
Dr James Colthurst, who met the princess on a skiing trip when she was 17, said marrying Charles brought his friend global fame, but that no one realised how popular she would be.
Writing in The Telegraph on what would have been Diana's 60th birthday, he revealed: "I felt, when she joined the Royal Family, she may not have been fully aware of the machine she was in.
"The Firm, for its part, was unaccustomed to having a superstar in its midst, and I don’t think it knew how to cope with the enormous amount of publicity she generated."
He said Diana "wasn’t given much of a brief at Clarence House" before the wedding.
Dr Colthurst, who helped Diana deliver her secret tapes to Andrew Morton in 1992 as he wrote her biography, said she "didn't have a big support team"and didn't seek adulation from fans, preferring interaction with people and to inject humour into the situation.
Despite the difficulties that plagued Diana through her marriage, Dr Colthurst said she seemed happy in her final months, before her sudden death in a car crash in Paris in 1997.
He said she had taken well to motherhood and enjoyed having her children around her.
He remembered her "infectious laugh" and said that her sons, William and Harry, had inherited "her sensitivity and caring".
His comments come on what would have been Diana's 60th birthday, as her sons prepare to unveil a statue of her in the Sunken Garden at Kensington Palace.
It's thought the small ceremony will only be attended by the princes and Diana's siblings, alongside some of those involved in its installation, like the sculptor Ian Rank-Broadley and the gardener Pip Morrison.
As the brothers prepare to unite, Dr Colthurst's comments may also seem to echo those made by Harry and Meghan during their interview with Oprah Winfrey in March 2021.
They said there was a lack of support for Meghan when she joined the family, and that she was denied mental health help when she had suicidal thoughts during her first pregnancy.
Harry also drew comparisons between his wife and his mother, suggesting that the palace was not ready for the press attention, particularly when they were on tour in Australia.
Harry said their 2018 tour "brought back memories" of Diana's success down under during the 1983 tour with Charles.
The Duke of Sussex returned to the UK over the weekend for the unveiling of the statue on 1 July and is reported to be having a sit down talk with his brother, the Duke of Cambridge, following the small ceremony.
Neither Kate or Meghan will be at the event, though William is said to have been preparing to show the statue to his children, George, Charlotte and Louis, before the formal unveiling.
Watch: Diana's favourite garden to be filled with 4,000 flowers for statue unveiling