King's film reveals his personal philosophy

In an unusually personal royal film, King Charles has asserted his belief in the need for human life to work in keeping with the natural world - saying he would not be deterred by critics or scepticism.

"This was the approach I was going to stick to, a course I set, and I wasn't going to be diverted," says the King, in the film Finding Harmony - A King's Vision, to be screened on Amazon's Prime Video next month.

The King will attend the film's launch on Wednesday - in the first premiere held at Windsor Castle, with the spectacular Waterloo Chamber turned into a makeshift cinema.

The King's spokesman said this was a different kind of royal documentary - without any gold carriages or glittering crowns.

Instead the golden thread running through the 90-minute documentary is the King's own philosophy of "harmony", that brings together environmentalism, religion, architecture, art and design.

He provides his own description: "It all boils down to the fact that we are actually nature ourselves, we are a part of it, not apart from it, which is really how things are being presented for so long," says the King.

The film, made in collaboration with his King's Foundation charity, is a sometimes elegiac look at his many decades of campaigning to protect the natural world.

He watches himself making a speech in 1970, aged 21, arguing the environmentalist cause. The accent might have been plummier, but his position has been remarkably consistent, even though he has faced mockery, saying that people thought his views were "bonkers".

Elsewhere in the documentary, narrated by Kate Winslet, he is described as a "bit of a hippie".

And the movie addresses one of the hardiest old chestnuts about the King - that he talks to plants - saying how the comments he has made about being close to nature became an opportunity to marginalise his views.

Although as the decades went by, with support for sustainability becoming mainstream, his views are seen as going from "crazy" to "common sense".

Putting ideas into practice has been an important part of his approach. Dumfries House in Ayrshire has been renovated and turned into a training centre in a part of Scotland hit badly by the closure of local coal mines.

The film shows how this project has become an important local asset and economic driver, providing jobs and skills, training 10,000 people a year.

Highgrove, a quirky and characterful house in Gloucestershire, that seems allergic to straight lines, has become a living laboratory for his organic gardening and farming techniques.

The King is seen in Highgrove feeding chickens and collecting eggs, in a shed called Cluckingham Palace.

He also gives a glimpse of the outside of his "sanctuary", a private place for his own personal reflection. Reflecting his deep interest in religion and spirituality, above the door is inscribed the prayer: "Lighten our darkness, we beseech thee, O Lord."

The inclusivity of his beliefs are also suggested as we see him at a fire ceremony, alongside indigenous peoples wearing elaborate headdresses, at an inaugural "Harmony Summit" last summer.

There are glimpses in the film of Prince William and Prince Harry in archive footage, along with childhood images of King Charles.

There is an unexpected appearance from the Duke of York. Although in this case it is the name of a variety of potato that the King recommends as a good choice for baking.

"If you want to have a decent baked potato, which I love, you've got to have the crispy skins, so the red Duke of Yorks are very good," he says.

The movie is promoting his world view about the interconnectedness of all things - and it is an example of how we are seeing more of the King as an inner man, beyond his role as a public figure.

It comes soon after an exhibition about another his personal passions, with his King's Foundation displaying examples of icons that are an important part of the Orthodox faith.

It is an eclectic and international vision, with the film sweeping around examples of harmony in places including India, Guyana and Afghanistan.

But it is also a world in which the US politician we hear from is former vice president Al Gore, who has campaigned on climate change.

The King makes his own observation about his life of campaigning.

"Maybe, by the time I shuffle off this mortal coil, there might be a little more awareness… of the need to bring things back together again," he says.