When the invite first came through inviting me to Buckingham Palace, I feared the worst. Obviously, I thought, the palace was angry at the recent controversy caused by my panel on The Crown or they’d discovered my teenage love of the Sex Pistols and were planning to send me to the Tower.

However, it turned out I had been invited to watch a documentary about the Queen’s latest environmental campaign including a landmark interview between Her Royal Majesty and Planet Earth’s David Attenborough in the palace gardens.

The ITV documentary, The Queen’s Green Planet, which is produced by ITN Productions, features a conversation between “two of the most consummate professionals on the planet” discussing the 1,400 trees planted in the Buckingham Palace gardens as well as the monarch’s new initiative to create a vast network of native forests across Britain and the Commonwealth – the Queen’s Commonwealth Canopy.

Walking through the gravelly entrance to the palace, filled with Beefeaters and armed guards, was a strange experience. It felt like walking into an episode of Netflix’s royal drama with an even bigger budget. Phones are confiscated at the entrance so there’s no photo evidence of me sneaking around the house, but wandering the halls of history is a strange and wonderful feeling, particularly for someone more used to covering the latest launch of Love Island or the BBC’s most recent crime drama.

The film highlights the Queen’s interest in trees but also how her ambitious global project has spread across more than 50 countries. The interview between the Queen and Attenborough is casual and fascinating, like watching two old friends out for a stroll. It also highlights the Queen’s humor, something I wasn’t expecting.

“That one, we won’t look at because it doesn’t seem to be doing very well,” she says, pointing to a small, disfigured tree. As Attenborough chuckles, she adds, “Are you sure that’s meant to be like that? Somebody sat on it I think, at the garden party.”

The Queen also takes a pop at the noise usually created by U.S. Presidents by their helicopters. As the pair are interrupted by a noise from the sky, she says, “Why do they always go round and round when you want to talk? Sounds like President Trump, or President Obama.”

The film also includes a rare interview with Hollywood A-lister Angelina Jolie with her children, planting trees on behalf of the initiative. “You sit up at night in a tent with your kids and they say, “Why does the Queen of England care about planting trees in Africa?’ She’s just this really lovely lady who really cares about the future, and she wants your grandkids and her grandkids to be able to be running around, enjoying nature. She thinks that really matters and I agree with her,” says Jolie.

After the screening of the documentary, which was attended by Sophie, Countess of Wessex, as well as ITV chiefs including Chairman Peter Bazalgette, Chief Executive Carolyn McCall and content chief Kevin Lygo, the broadcaster’s Controller of Factual Jo Clinton Davis, who commissioned the film, spoke alongside exec producer Chris Shaw and director Jane Treays.

Clinton Davis said, “Rare is the project that gets pitched and we say yes immediately. It’s a landmark piece with a rare piece. The scope of this… it takes root, literally. It has the potential to speak to future generations.”

The documentary took nearly two years to make and the interview between Attenborough and The Queen lasted around 90 minutes, all done without a script.

Treays, who called it the “most magical moment of my career”, said it was a day “full of expectation and joy”. “The Queen is extremely observant and very interested. We had time to stop and bring that out. It was a beautiful day and everyone was on great form,” she added. “David Attenborough is incredible at charming all of the ladies.”

ITN’s Shaw admitted that when the company was first discussing the doc, it didn’t feel that promising “because environment projects are difficult to get to large audiences. But these two iconic figures make it an accessible film”.

ITN and its distribution partner Cineflix Rights is now hoping to get a U.S. sale for The Queen’s Green Planet after the latter launched it at Mip TV. Chris Bonney, CEO, Rights, Cineflix Media, said, “Royal documentaries sell really well internationally, particularly when younger royals are featured – in this case Prince William and  Prince Harry alongside the Queen.  Add in David Attenborough, one of the world’s most respected broadcasters, a global superstar in Angelina Jolie, a critically acclaimed director in Jane Treays, and you have in The Queen’s Green Planet a high quality, globally appealing film which is a step above other royal documentaries on the market.”

The Queen’s Green Planet airs Monday 16 April at 9pm on ITV.