“Robert would be ideal, though he is already aligned with his own family’s brand, so it will take some negotiating,” explains the source.
While Thor star Chris might seem more at home on the set of a big-budget Hollywood blockbuster than trawling through the jungle or bush, the 39-year-old actor loves nothing better than being in the great outdoors.
He also teamed up with National Geographic recently on a six-part Disney+ documentary called Limitless, which really caught David’s team’s eye.
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“Chris has proved his mettle as a documentary host,” says our source.
WATCH: Limitless with Chris Hemsworth Official Trailer
Having grown up with Africa as his second home and coming from a long line of passionate environmentalists, Prince Harry could also be the perfect choice to take over from David.
After stepping down from his role as a full-time working royal in 2020, Harry is on the lookout for new ways to earn a crust.
“Harry would have been the top pick, being British, doing so much conservation work in Africa, and having a long-time friendship with David through the royal family,” explains our source.
However, things became a bit “complicated” when the 38-year-old prince’s wife, Meghan Markle, got involved in negotiations.
WATCH: Prince Harry criticises climate change deniers
“Meghan fancied the idea of her and Harry as a duo rather than just Harry carrying on David’s legacy,” says the source. “Once it became clear that one was not an option without the other, they went back to the drawing board.”
“So far, Chris is in the lead, with Robert being a very, if not slightly more complicated, second.”
One thing is clear for whoever steps into David’s shoes: they’re going to have their work cutout for them. “[David is] a legend and an irreplaceable one-off,” says the former head of the BBC’s Natural History Unit, Wendy Darke.
David promises that it will all be more than worthwhile. “Having spent all my life trotting around the world and getting other people to pay for it in order to see the most wonderful things you could ever wish to see – how could I not but say that was a perfect career?” he says.
For more, pick up the latest issue of New Idea!