Charles At 70&will air on BBC One on Thursday - and the programme sees both Princes William and Harry discuss their childhood.
Litter-picking in East Anglia is few people's idea of a dream family holiday.
At the evening's State Dinner, Prince Charles spoke of the bonds between the people of the United Kingdom and The Gambia, saying, "We have also been fortunate to meet so many people who are making a profound difference to this partnership, whether British or Gambian or, indeed, one of the countless people who have a home in both countries and are, in so many ways, a living bridge between us".
"We're there with our, basically, spikes, stabbing the rubbish into black plastic bags".
Prince Charles and his wife Camilla, the Duchess of Cornwall, are taking a page from sons William and Harry and their wives by posing in a series of intimate photos for Vanity Fair to complement the magazine's candid interview with the heir apparent.
He went on to speak to Harry and Meghan's official wedding photographer, who described Charles and Camilla as like "a young couple in love", while Camilla's nephew even contributed and recalled their "genuine, deep-down affection and love", painting a picture of a couple very much in love.
"I used to get taken the mickey out of at school for just picking up rubbish", he says, warming to the litter-picking theme.
Charles is well known for his campaigning to protect the rain forests, save endangered species from extinction and combat the threat of climate change.
In the documentary, William spoke alongside his brother the Duke of Sussex as they watch a screening of a speech Charles gave in 1970, warning of the dangers of plastic waste.
"He does live the way he advocates so, until someone comes up with an electric plane - it's impossible to get round the world, for instance, without using a plane that's there", he said.