It was a bold move designed to revive public interest in the Royal Family, ushering them into the modern age by showing them as ordinary people.
But it turned out that seeing Prince Charles chopping lettuce and making salad dressing for a family barbeque while the Duke of Edinburgh struggled to brown the sausages also destroyed their mystique.
In 1972, the Queen ordered the BBC’s infamous fly on the wall documentary to be locked away and it has never been seen in full since - until now.
The 90-minute documentary, Royal Family, was uploaded onto YouTube earlier this month and has already been seen thousands of times, ensuring the hallowed footage is no longer one of television’s great secrets.
And more than 50 years later, Buckingham Palace’s stance on it remains unchanged.
A royal source said: "This is a matter for the BBC. From time to time, things pop up on the internet that should not be there. We will assume it’s going to be taken down."
The BBC declined to comment but is understood to be seeking to have it removed from the web.
A BBC source said: "We will approach YouTube to have it removed. We always exercise our copyright where we can.
"However, it is notoriously difficult to chase these things down on YouTube once they are out there. Anybody can download it and you just end up chasing your tail."
It is unclear how or why Richard Cawston's film, thought to be protected by Crown copyright, has suddenly reemerged more than 50 years later.
One version appears to have been uploaded on January 15 by a new account in the name of Philip Strangeways, referencing a mystery organisation called HM Government Public Service Films.
First broadcast by the BBC, and a week later by ITV, the documentary offered the public an unprecedented glimpse into the private world of the royals, showing them watching television, having a picnic and rowing boats on a lake (seen below).
Three-quarters of the British population watched it in June 1969, and it was replayed repeatedly on television before being pulled from view.
The camera crew spent 12 months filming and it was deemed to have had such an impact that the Queen chose not to give a televised Christmas speech that year, issuing a written message instead.
The film opens with Prince Charles waterskiing, cycling and fishing, later cutting to the Queen feeding her horses carrots after Trooping the Colour, opening letters at her desk (pictured below) and suggesting to a member of staff there is "much too much about history" in a speech she is reviewing.
Lunch, served at 1pm, is pushed on a trolley from the Buckingham Palace basement "200 yards of corridors and then up in a lift two floors" to the Queen’s apartments.
In one scene, the Queen discusses outfits with her dresser, looking at patterns - "this one, one might possibly keep for Australia" - tiaras and jewellery.
She admires the "fascinating" Timur ruby necklace, telling her dresser: "I think really, one should get a dress designed especially so that one could wear it."
Several scenes show the Queen and the Duke of Edinburgh in transit, reading newspapers on the Royal Train (and admiring a cartoon) and lamenting their Portuguese on the way home from a tour of Brazil and Chile.
Many traditions are reassuringly familiar, such as the annual summer garden parties which have barely changed. At one point, the Duke asks a decorated war veteran with typical humour: "What’s that tie? Alcoholics Anonymous?"
In another scene, the Queen takes four-year-old Prince Edward to a local grocery store (pictured below) and buys him an ice cream with cash from her purse, later expressing concern about the mess it will make in the car. The young prince is also taken rowing by his father and practises his reading on camera.
The documentary shows the Queen perfecting the art of small talk with guests, telling US President Richard Nixon: "World problems are so complex, aren't they now?"
According to one Royal biographer, the Queen regretted her decision to allow the cameras in and it came to be seen as a "reinvention that went wrong".
Sir David Attenborough, then a BBC controller, is said to have told Mr Cawston the film was "killing the monarchy".
The Princess Royal made her disdain for the film clear, once saying: "I never liked the idea of Royal Family, I thought it was a rotten idea. The attention which had been brought upon one ever since one was a child… you just didn’t need any more."
In 2015, footage of the Queen, aged about seven, performing what appeared to be a Nazi salute was obtained by The Sun.
Buckingham Palace said at the time that it was "disappointing that film, shot eight decades ago... has been obtained and exploited".
The black and white footage, lasting about 17 seconds, showed the Queen playing with a dog on the lawn in the gardens of Balmoral before the Queen Mother raised her arm in the style of a Nazi salute, mimicked by the Queen.
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