Netflix's The Crown returned to our screens at the weekend with season four, marking Olivia Colman's second outing as Queen Elizabeth II.
Joining The Crown cast this series are Emma Corrin (Princess Diana) and Gillian Anderson (Margaret Thatcher), who take centre-stage to play the two most-talked about figures of the 1980's as Britain approaches the back end of the 20th century.
Princess Diana and Prince Charles' marriage and its gradual decline are covered in great detail throughout season four, with viewers meeting the teenage Diana in episode one along with her formidable grandmother Lady Fermoy, who trains the future Princess in the run-up to her wedding.
But who was Lady Fermoy? And how accurate is the series' portrayal of her?
Here's everything you need to know about Princess Diana's grandmother and The Queen Mother's lady-in-waiting.
Want to know what we made of season four? Make sure to check out the RadioTimes.com review for The Crown.
Who was Diana's grandmother Lady Fermoy?
Ruth Roche, the Lady Fermoy, was Princess Diana's maternal grandmother and lady-in-waiting and friend to The Queen Mother.
She married Maurice Roche, the 4th Baron Fermoy, in 1931 and had three children – one of whom was Frances Shand Kydd, Diana's mother.
According to the Independent's obituary of Lady Fermoy, she testified against her own daughter during her divorce in 1969 from Viscount Althorp John Spencer – Princess Diana's father – which resulted in Althorp being granted custody of their children.
"By siding with Norfolk aristocracy rather than her own flesh and blood, she changed Diana's life forever as the judge gave the Earl charge of his four children," The Telegraph wrote.
Lady Fermoy was a concert pianist and founded the King's Lynn Festival in 1951, which The Queen Mother became a patron of.
After the death of her husband, Lady Fermoy was appointed as an Extra Woman of the Bedchamber in 1956, and was soon promoted to Woman of the Bedchamber four years later.
She was a close friend of the Queen Mother and member of her court, accompanying her on private visits to France and Venice.
Lady Fermoy died on 6th July 1993 at the age of 84.
Who plays her in The Crown?
Scottish actress Georgie Glen, who is best known for her roles in Waterloo Road, Little Britain and Call the Midwife, plays Lady Fermoy in The Crown's fourth season.
She is introduced as Diana's formidable grandmother and close friend of The Queen Mother, who accompanies Diana (Emma Corrin) on her dates with Prince Charles (Josh O'Connor) before their engagement.
The Baroness comes across as a strict and cold grandmother with a strong loyalty to the Royal Family in the series, telling Diana during her first trip to Balmoral that it is "the most important weekend of [Diana's] life".
In the third episode, Lady Fermoy is enlisted as Diana's royal etiquette coach in the run up to her marriage to Prince Charles, putting the young woman through her paces as she teaches her who to curtsey to and in which order.
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Did she 'train' Diana for royal life after the engagement?
While it is unknown whether Lady Fermoy did in fact give Diana royal lessons, many would assume that Fermoy would have given her advice considering her closeness to the Royal Family.
However, the close companion of The Queen Mother had apparently discouraged Diana from marrying into the Royal Family according to Diana's biographer Andrew Morton, who writes that Fermoy told her granddaughter: "Darling, you must understand that their sense of humour and their lifestyle are different, and I don't think it will suit you."
In an article in The Telegraph, Morton wrote that Diana later realised that Lady Fermoy's advice had not been for her sake, but for Charles' as she "did not consider her an appropriate match for the future King".
It is also reported that Princess Diana and her grandmother did not get along, with Diana's private secretary describing Fermoy as "an attitude which was anathema to the Princess".
When the marriage between the Prince and Princess of Wales began to disintegrate, Lady Fermoy apparently believed that the couple should stay together to prevent a scandal from embarrassing the Royal Family.
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Former Archbishop of Canterbury Robert Runcie told The Times in 1996: "Ruth was very distressed about Diana's behaviour. She was totally and wholly a Charles person, because she's seen him grow up, loved him like all the women at court do, and regarded Diana as an actress, a schemer."
It was reported that Lady Fermoy and Diana were not on speaking terms following the 'War of the Wales', however Morton claims that they finally made peace with one another shortly before the 84-year-old passed away in 1993.