Whether you're a British monarchy enthusiast, a history buff or old enough to remember the events that play out on screen, many of The Crown's viewers are well-versed in the events and narratives that it has covered across its four-season run.
From the assassination of Lord Mountbatten to Charles and Diana's tumultuous relationship to Michael Fagan breaking into Buckingham Palace, the latest chapter once again delves into a raft of extraordinary, widely-publicised moments that are certain to ignite a renewed interest.
Another such story is that of Katherine and Nerissa Bowes-Lyon, which some will be familiar with, but equally, there will be many who aren't.
In episode seven, 'The Hereditary Principle', Princess Margaret (Helena Bonham Carter) makes a devastating discovery that once again paints the royal family in a less than flattering light.
During a session with her therapist, Margaret is told about "the sisters", of which she had no knowledge.
Katherine and Nerissa were the first cousins of Margaret and Queen Elizabeth II, and the third and fifth daughter of their mother's eldest brother, John Herbert "Jock" Bowes-Lyon and his wife Fenella.
"[They were] locked up in the Earlswood Institution for Mental Defectives (later changed to The Royal Earlswood Hospital), if you please, in Redhill, [Surrey]," says Margaret to her sister in episode 7.
Elizabeth (Olivia Colman) tells Margaret that they were "long dead", and she believed that to be the case.
"It's my understanding that they're both very much alive," Margaret responds.
The pair consult Burke's Peerage and see their deaths were both recorded, in black and white – but that was entirely false.
According to reports, the pair were sent to Earlswood in 1941 when Nerissa was 22 years old and Katherine was just 15.
They both had severe learning difficulties, and never learned to talk during their lifetimes.
In Channel 4 documentary The Queen's Hidden Cousins, which aired back in 2011, hospital carers said that whenever members of the royal family appeared on television, Katherine and Nerissa would stand up and salute or curtsy.
When the hospital opened, it was believed to be ahead of its time, dedicated specifically to helping individuals like Katherine and Nerissa. But it was later criticised for sanitation problems and overcrowding.
Speaking to Channel 4, the nurses who worked there and relatives of other residents painted a fairly miserable picture of the institution, its staff tasked with looking after large numbers of patients.
The Telegraph reported that the royal family paid £125 per year to the institution, but that was the extent of their involvement in Katherine and Nerissa's lives.
In The Queen's Hidden Cousins, viewers were told that there was no acknowledgement of their birthdays by relatives and they didn't receive any cards at Christmas.
A hospital representative of Katherine told Thames News in 1987 that the last time she was visited "by direct relatives [was] in the early '60s", as far as he was aware.
But she was visited by volunteers and enjoyed holidays at the hospital's other home, among other places.
Lady Elizabeth Anson, a niece of the two sisters, issued a statement in which she denied the claim that they didn't receive visitors.
She also said that "there was no attempt at a cover-up" and her grandmother was "a very vague person who often didn't fill out the forms that Burke's Peerage sent her, either properly or completely."
The AP reported that in 1987 Brian Rix, then-head of the Royal Mencap Society, said that the Queen Mother learned about the fate of her nieces in 1982, believing them to be dead up until that point.
It should also be noted that in 1986, the Queen Mother became patron of the charity, which describes itself as "the leading voice of learning disability".
Nerissa died in 1986, aged 66. The Telegraph reported that hospital staff were the only people present at her funeral, and her initial grave had plastic tags and a serial number, rather than a tombstone.
Katherine passed away in 2014 at the age of 87, by which time their story was widely known after the details became public in 1987.
According to a report in the Daily Express from 1996 (via AP), the administrator of the hospital, Peter Kinsey, contacted the next-of-kin of all of its patients to inform them that it was shutting down.
Both the Queen and the Queen Mother were among the recipients of that news and were invited to discuss Katherine's future, but Buckingham Palace had no comment and the pair did not attend.
"It is a matter for the Bowes-Lyon family," read a Buckingham Palace statement in response to a report about the sisters published shortly after Nerissa's death.
There were also other relatives of the royal family living at the institution.
Katherine and Nerissa's cousins, Idonea, Etheldreda and Rosemary Fane, the children of Fenella's sister, were also housed there.
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