Speaking to Sky News to mark the launch of his environmental Earthshot Prize, William confessed that whilst watching the documentary about extinction, his son told him: "I don't want to watch this any more."
WATCH Prince William talk about son George in candid interview
When asked about the importance of optimism and whether he tried to bring it into discussions with his family, the father-of-three replied: "I think to be perfectly honest I'm struggling to keep the optimism levels going with my own children, and that's really kind of like… an understanding moment.
"Where you kind of look at yourself and go 'Am I doing enough on this, are we really at this stage in life when I can't be hugely optimistic and pleased that my children are getting so into nature.'
"Because you kind of worry and dread they're soon going to realise that we are in a very, very dangerous and difficult time in the environment and that as a parent, you feel you're letting them down immediately."
Prince George and his siblings recently met David Attenborough
William went on to say how his children were fans of Sir David Attenborough's natural world documentaries but the watching the recent documentary A Life On Our Planet was too much for George.
"The most recent one – the extinction one – actually George and I had to turn it off, we got so sad about it halfway through. He said to me 'You know I don't want to watch this anymore'.
The Cambridges are big fans of the broadcaster
"Why has it come to this and you know he's seven years old and he's asking me these questions already, he really feels it, and I think every seven-year-old out there can relate to that."
George and his siblings, Princess Charlotte, five, and Prince Louis, two, are big fans of the broadcaster and recently quizzed the 94-year-old in a video recorded at Kensington Palace.