Meghan Markle told a friend Buckingham Palace's attitude towards her difficulties was like a "death by a thousand cuts", according to biographer Omid Scobie.
Omid Scobie was the co-author of the biography Finding Freedom: Harry and Meghan and the Making of a Modern Royal Family.
Writing a piece in Harper's Bazaar, he claimed Meghan felt her and Harry's public image was not considered important.
He mentioned reports she had made Kate Middleton cry - an incident Meghan told Oprah was actually the other way around.
Scobie claimed the Duchess of Sussex's well-being deteriorated as the institution did not intervene or defend her amid negative claims about her.
He said multiple people close to the royal couple said they felt unsupported and unprotected by the institution.
Do you enjoy reading about the royal family? Sign up for all the best royal news from the Mirror here
He said: "Meghan later likened the experience to a friend as 'death by a thousand cuts.'
"Her reference to an ancient Chinese execution method was no coincidence."
Palace aides also allegedly told Meghan's friends to stay silent.
But Scobie claimed when allegations about the couple being unsupported were put to the Palace for a response for his biography, they seemed 'baffled' by the Sussex's claims.
A senior aide told Scobie: "'This is nonsense...We did absolutely everything [for Meghan].
When Scobie asked for examples he says he was told: "Everybody welcomed her.
"And she was given all the support she needed.
"They forget how accommodating we were when it came to navigating the duchess through her first steps [as a working royal]."
A statement issued by Buckingham Palace on behalf of Her Majesty The Queen, responding to Meghan and Harry's bombshell interview with Oprah Winfrey, said: "The whole family is saddened to learn the full extent of how challenging the last few years have been for Harry and Meghan.
"The issues raised, particularly that of race, are concerning.
"Whilst some recollections may vary, they are taken very seriously and will be addressed by the family privately.
"Harry, Meghan and Archie will always be much loved family members."
