Queen Elizabeth II's late sister, Princess Margaret, reportedly, had "serious hatred" for Princess Diana. She even took this ill will to her grave as she never forgave her nephew's wife even in death.

Geo News reported that Craig Brown, who penned "Ninety-Nine Glimpses of Princess Margaret," made the allegations in 2018. He asserted that the royal-born Princess was "very unforgiving," adding that she passed away with "despise in her heart."

The Countess of Snowdon was allegedly never the forgiving type of person. This was said to be especially true when someone "crossed swords" with her.

In the same interview the royal biographer did four years ago, he, also, shared that Princess Margaret "scoffed" at the idea of Princess Diana having a statue outside Kensington Palace. He claimed that the late royal-born Princess would not like to have "that woman outside [her] bedroom window," according to Express UK.

Brown continued that the Queen's sister was a "very difficult woman" during her time. But, her hatred for the Princess of Wales emerged after witnessing Prince Charles' then-estranged wife's interview with Martin Bashir for BBC Panorama in 1995.

The Countess of Snowdon allegedly was "not keen on others misbehaving." Furthermore, she saw her nephew's former wife's "broadcasting" of feelings to the world without a warning as an "amazing kind of betrayal, even if what Diana was alleging was true."

The royal author, later on, asserted that Princess Margaret would not have spoken to Princess Diana even if they both had lived for another 30 years.

The royal-born Princess might have hated the Princess of Wales after her 1995 interview but, reports said that they were once "firm-friends." There was even "sympathy on [Princess] Margaret's part" following the Wales couple's bitter separation, according to Tatler.

Andrew Morton revealed that the Queen's sister saw herself and the then-wife of Prince Charles as "two metropolitan princesses" as neither of them "were hunting, shooting, or fishing types." She took her nephew's then-young partner, as well, "under her wing, accompanying her to go shopping, or to the theater, or just on social engagements."

Princess Diana, also, allegedly told the royal biographer that she had always "adored Margo," adding that she loves her "to bits'' as "she has been wonderful to [her] from day one." Moreover, it was stated that Princess Margaret was the one who came to the young royal's aid when she was struggling in her new role in the British Monarchy.

However, things went down south after the 1995 bombshell interview. The Countess of Snowdon reportedly saw it as a "betrayal" not only to the monarchy but to her sister, Queen Elizabeth II herself, as well.