EXCLUSIVE: How Princess Diana's Mother 'Turned Against Royals After Daughter's Death'

Princess Diana's mother became so embittered by her family's treatment following her daughter's death she turned against the monarchy and declared herself a republican, according to royal biographer Ingrid Seward.

RadarOnline.com can reveal Frances Shand Kydd, who died aged 68 in 2004, spent her final years increasingly isolated on the Scottish island of Seil after Diana was killed aged 36 in Paris in August 1997.

Seward now reveals in her new book Catherine & Diana – due for release on September 24 and adapted by the Daily Mail ahead of it hitting shelves – how Shand Kydd's resentment toward the Windsors deepened amid disputes over Diana's funeral and her subsequent contact with grandsons Prince William and Prince Harry.

Seward writes Shand Kydd told a friend: "The Royal Family are a disgrace. All duty, tantrums, coldness and selfish callousness. When I got away from that lot, it was wonderful – I felt free."

Her anger represented a remarkable reversal for someone once closely connected to royal life.

Shand Kydd's first husband, John Spencer, later Earl Spencer, had been an equerry to Queen Elizabeth II, while her mother, Ruth Roche, Lady Fermoy, served the Queen Mother as Woman of the Bedchamber for 33 years.

Diana spent part of her childhood on the Sandringham estate and played with Prince Andrew and Prince Edward.

But Seward writes that relations deteriorated dramatically and Shand Kydd was particularly hurt after Diana's death. Shand Kydd added: "The Queen did not get in touch after Diana's death. I did not see or hear from her."

Seward also writes Diana's death traumatized her mother, whose health deteriorated afterward and who temporarily lost the power of speech.

Relations were complicated further by Shand Kydd's concerns about William and Harry following their mother's death.

She sought a meeting with their father, then-Prince Charles, and traveled to Highgrove in July 1998, hoping to establish how she would remain involved in her grandsons' lives.

Seward writes four years later she remained unhappy about her access to William and Harry, saying contact had largely consisted of emails and letters. Her frustration ultimately hardened into hostility toward the institution she had once known intimately.

She was also angered by arrangements surrounding Diana's funeral at Westminster Abbey.

Shand Kydd claimed: "We almost boycotted the service. We had to fight for what we got."

She recalled disagreements over music and the requirement that the Spencer family repeatedly stand as senior royals arrived.

Diana was eventually buried at her family's Althorp estate, where the Spencer flag replaced the Royal Standard at the graveside.

Seward writes that Shand Kydd never escaped the consequences of her daughter's death. Thousands of letters arrived at her secluded home, including threats and abusive material.

During her final years, Shand Kydd described the lasting emotional toll of Diana's death.

She told a friend: "I no longer pray for peace because I know I won't get any. I just pray instead for the ability to cope."

A royal source claimed: "Frances had once been completely comfortable around the Royal Family, so her transformation was extraordinary. Diana's death was the breaking point. She felt her daughter had been badly treated in life and that the Spencer family was pushed aside even after her death.

"What particularly wounded Frances was the feeling that nobody at the highest level of the Royal Family had reached out to her as Diana's mother. Whether others saw events differently or not, Frances regarded that silence as deeply cold.