Who was Ruth, Lady Fermoy? According to a leading biographer, Diana’s grandmother was “the most terrible woman” he had encountered during his research.

According to the late biographer and journalist Anthony Holden, Ruth was not without flaws.

Or, to put it more honestly, she was, as he put it, ‘the most horrible woman I have encountered in my research’.

Whatever else she was, Diana’s grandmother was a deeply influential figure at court, a friend and confidante of the last Queen Mother, whose views had a profound influence on the future Princess of Wales.

It has been suggested that Lady Fermoy was among those who conspired to engineer a dynastically beneficial but inappropriate marriage between her granddaughter and the future king – although she denied this.

She certainly took an uncompromising stance when her daughter, Frances, left Johnny Spencer and the family home, sided with Spencer, not Frances, and appeared in court to make the case.

Lady Fermoy was born Ruth Sylvia Gill in October 1908, the son of wealthy Scottish landowners Colonel William Smith Gill and his wife Ruth.

It is believed that Lady Fermoy had Armenian and Indian ancestry. During her youth, Ruth showed early promise as a pianist and studied with the famous French virtuoso and scholar Alfred Cortot at the Paris Conservatory in the 1920s.

But her musical career came to a standstill when she married the wealthy and much older Maurice Roche, 4th Baron Fermoy, on 17 September 1931 at St Devenick’s Church in Bieldside, near Aberdeen.

Together, Lord and Lady Fermoy had three children, including Frances – later Frances Shand Kydd – the mother of Diana, Princess of Wales.

Lady Fermoy was known for her fastidious adherence to social rules and believed particularly strongly in the sanctity of marriage.

This was so much so that when Johnny Spencer, then Viscount Althorp, sued for custody of Diana and her siblings in 1969, their grandmother supported him.

Lady Fermoy had left her husband for another man – and Spencer won.

Her royal connections began in 1956 when she was appointed ‘Additional Lady of the Bedroom’ by the Queen Mother, who had lost her husband just four years earlier.

Lady Fermoy was introduced to the role through her own husband, who regularly went on shoots with King George VI but had died in 1955.

The Queen Mother, as she was now known, would prefer to appoint widows like her to the household.

Promoted to ‘Lady of the Bedroom’ in 1960, she held this position for the next 33 years.

Lady Fermoy would do that spend a lot of time with the Queen Mother at Royal Lodge, as well as at Clarence House.

For this reason, it was widely speculated that the two women had ‘entrapped’ their respective grandchildren, the Prince of Wales and Lady Diana Spencer.

However, when asked about it, Lady Fermoy commented: ‘You can say that if you like, but it simply wouldn’t be true’.

She reportedly dissuaded her granddaughter from the union, saying, “Honey, you have to understand that their sense of humor and their lifestyle are different, and I don’t think it will suit you.”

Diana’s biographer Andrew Morton wrote that Diana had later realized that Lady Fermoy’s advice had not been for her sake, but rather for Charles’s, as she “did not consider her a suitable match for the future king.”

After her husband died, Lady Fermoy resumed her interest in piano and piano, particularly with Josef Krips in 1950 and with Sir John Barbirolli in 1966.

She founded the King’s Lynn Festival in 1951 and remained closely involved with the festival for 25 years, convincing the Queen Mother to become its patron.

She was appointed Commander of the Royal Victorian Order in June 1966 and Dame Commander of the Royal Victorian Order in June 1979.

Lady Fermoy died on 6 July 1993 at her home at 36 Eaton Square, London, aged 84.

It was reported that she did not speak to Diana after the ‘War of the Waleses’ as Lady Fermoy reportedly believed the couple should have stayed together to avoid scandal.

Former Archbishop of Canterbury Robert Runcie told The Times in 1996: ‘Ruth was deeply disturbed by Diana’s behaviour.

“She was very much a Charles person, because she watched him grow up, loved him like all women at court, and considered Diana an actress and a schemer.”

However, Morton claimed they had made peace with each other shortly before the 84-year-old died.

Lady Fermoy was reintroduced to a global audience in the Netflix series: The Crown, where viewers met teenage Diana along with her formidable grandmother as she trains the future princess in the run-up to her wedding.

Scottish actress Georgie Glen, best known for her roles in Waterloo Road and Call the Midwife, played Lady Fermoy in the fourth season of The Crown.

Although it is not known whether Lady Fermoy gave Diana royal lessons, many assumed this was the case given her close relationship with the royal family.

Her role in Charles and Diana’s lives has come to the fore again with the recent death of Anthony Holden, whose second biography of the future King Charles in 1988 was the first to expose the emptiness of his marriage to Diana.

In the book, he wrote, Diana “has a husband who no longer understands her? it seems she doesn’t even love her very much’ – and an insight that came well before Andrew Morton’s Diana: Her True Story lifted the lid on the couple’s miserable life.)

It caused a firestorm, with friends of Charles denouncing Holden for venting fantasies and one of his senior aides making public the book, published on the prince’s 40th birthday, describing it as ‘fiction from beginning to end’ .

Later events would, of course, prove Holden absolutely right.