Now, the photographer who took photos of the moment inside the Drawing Room at the Scottish estate, has revealed how the Queen was behind the scenes.
Jane Barlow, a Press Association photographer, was behind the lens that day, and ultimately ended up taking the last official photo of Queen Elizabeth II.
Before the Conservative Party leader arrived, Barlow said she spent a brief period alone with the Queen when she managed to snap a portrait of Her Majesty solo.
"I was there to photograph her meeting the new prime minister but for me the best picture was the one of the Queen on her own. And it has obviously become more significant now," Barlow told PA.
"I got a lot of smiles from her."
Barlow added the Queen "certainly did look more frail than when I photographed her in the summer," but that she appeared in "good spirits" and made small talk about the gloomy weather.
While the Queen's cause of death is yet to be revealed, an expert has pointed out a worrying detail on her hands in the final photos that signals what she could have been suffering from.
"It looks like there is possibly evidence of peripheral vascular disease. It's a blood circulation disorder that causes the blood vessels outside of your heart and brain to narrow, block, or spasm," Dr Deb Cohen-Jones told Daily Mail.
"It can sometimes result in heart failure. If your peripheral circulation is that poor, organs aren't receiving a good blood supply. It can be a sign of multi-organ failure."
Sadly, it is likely the disease would have caused the Queen "a lot of pain" as the images pointed to the illness being severe.
Despite the Queen generally enjoying robust health over her long life, concerns were sparked last October after she spent a night in hospital, going on to cancel a series of planned engagements, including hosting world leaders at the UN climate change summit in November.
She also came down with Covid-19 earlier this year.
Her appearances over the last few months then had been rare, although she returned to public duties before the start of her record breaking 70th year as monarch, which warranted a four day celebration in June.
The Queen spent recent weeks at her beloved Balmoral, where she died peacefully on Thursday.