CANNES • An avalanche of royal documentaries is set to sweep television schedules across the world in the run-up to the marriage of Britain's Prince Harry, 33, and American actress Meghan Markle, 36, next month.

"The world has gone crazy for the royal wedding," said Nick Bullen, the king of British royal TV, who has nearly nine hours of programmes in the pipeline for National Geographic, America's Fox network and Britain's ITV.

Rival shows such as Invitation To A Royal Wedding, about the behind-the-scenes planning for the big day, are among a raft being snapped up by buyers at MIPTV, the world's top TV market in Cannes, France.

"Kate and William was big," said Mr Bullen, head of Spun Gold TV, referring to the 2011 wedding of Prince Harry's brother and sister-in-law.

"But the Meghan factor has been huge. This is now an American story, one of their own, an American princess," he added.

"The last American to marry into the royal family was Wallace Simpson and look what happened there. That was quite a big world story."

Markle is like nothing the British royal family has ever seen before, said Mr Bullen.

"We now have a divorced mixed-race actress. She is beautiful, clever and opinionated. She is bringing something to the House of Windsor that has been missing for an awful long time. She is making the Windsors feel relevant to an audience that hadn't considered them before."

African and ethnic minority audiences are relating to the royals in a way they never did before, he said.

That comes on top of "the whole new generation who have been brought to the royals" through the runaway success of The Crown, online platform Netflix's No. 1 series, he added.

"The Queen's Wikipedia page has reported record traffic after The Crown, as viewers check the plot with the facts," he said.

His company's history of the family, The Royal House Of Windsor, has also been a surprise hit on Netflix.

Mr Bullen, whose company won a Bafta award for its documentary on the Queen's 90th birthday, said that for royal programmes to work, they had to have real insight.

"We don't make toadying TV, some people have. But in a world of fake news, you need truth at the heart of it and if you have that, you have a hit show."

But he admitted that the palace had to be kept onside for his company "to keep making these programmes. We keep them in the loop. You have to play with a very straight bat".

Among the other new royal documentaries being previewed at Cannes is a highly unusual and unexpectedly touching portrait of the Queen.

The Queen's Green Planet reveals her lifelong passion for trees, with a "relaxed and funny" monarch taking naturalist David Attenborough on a tour of the gardens of Buckingham Palace.

The pair, both 91, were born within three weeks of each other and have a wonderful screen chemistry, said director Jane Treays.

"They laughed and were quite playful with each other. They have known each other a long time and, because of that, we see quite surprising things like her real passion for trees.

"She has spent her life planting trees and so have her ancestors. It was very beautiful and touching to see how she relates to them and how much they mean to her. She has a particular love of some London plane trees planted by Queen Victoria", her great-great-grandmother.

The film, made by ITN to highlight the Queen's bid to build a network of global protected forests, will be broadcast in Britain next Monday.

In one hilarious moment, she reveals how her huge collection of new varieties of plants came about.

"I've been quite difficult to give presents to," she quips, "so they've said, 'Oh, let's give her a plant.'"

AGENCE FRANCE-PRESSE