Harry and Prince William "litter picking" during the school holidays, at explosive 60-minute BBC documentary about his life will reveal.
The movie, released to commemorate Charles' special birthday this month, is set to air on Thursday, November 8 at 9pm.
Prince William makes the extraordinary revelation, saying his father, Prince Charles lives "the way he advocates" when it comes to his environmental beliefs.
Prince Charles is renowned for his environmentalist stance and has long been an ardent campaigner for the planet.
Recalling the memory, William revealed: "He took us litter picking, when we were younger, on holiday.
"We were in Norfolk on school holidays and went out for litter picking with him.
"Both of us thought 'This is perfectly normal, everybody must do it'.
"We're there with our, basically, spikes, stabbing the rubbish into black plastic bags."
Harry said he was "programmed to collect litter because of the positive influence of his father.
He then praised his father for doing "an amazing job" and guiding them "without telling us what we should do".
The Duke of Sussex said: "He's done an amazing job without telling us what we should do.
Mummy, to the point where I mickey taken out of the nature of the job.
"I did not go out consciously looking for it.
"If you go for a walk somewhere and see something and it stands out, you pick it up.
"You really, I've literally done this because I'm programmed to do it because my father did it and in fact we should all be doing it."
William went on to say that his father was affected by the backlash he received for his environmental views, which saw him ridiculed for supposedly talking to plants.
He said, "He does live the way he advocates so, until someone comes up with an electric plane – it's impossible to get around the world, for instance, without using a plane that's there.
"He did take to heart the criticism quite a lot when he was younger".