A new Prince William documentary has given royal fans a sneak peek into the environmentalism he holds close to his heart.

Prince William: A Planet for Us All was filmed over two years and explores William's " personal mission to find ways to protect the natural world for future generations".

In the documentary, Prince William is seen travelling around the UK and internationally, visiting Tanzania and Pakistan.

The film was aired on ITV on Monday night and also includes previously unseen photos of his three children, Prince George, Princess Charlotte and Prince Louis.

George and Charlotte are seen in the film helping out with gardening while Louis is on a beach with a sand bucket.

William took some time to reflect on how fatherhood motivated him to use his platform to protect the environment.

"Now I've got George, Charlotte, and now Louis, your outlook does change and that's why I had to do something," he says in the documentary.

"I really felt like by the time my children were 20, at the rate poaching was at, there may not have been another rhino in the world."

He also is aware of the criticism this documentary will receive, saying that "someone has got to put their head above the parapet and say 'I care about this'".

He also speaks about teen climate change activist Greta Thunberg, who constantly receives criticism for her work. 

"People were desperate for someone to come along. Thank goodness there's somebody there with a young voice being active," William says.

"That generational gap has to be breached, somehow, so that the older political leaders understand that the younger generation mean business. They want their futures protected."

Despite some fans loving the documentary, others were quick to point out the family's love of grouse hunting in the UK.

"Interesting that Prince William says he wants to help save wild animals and the planet despite taking his young children on a lovely family hunting trip a few weeks ago," another said.

"Won't take Prince William seriously until he stops blasting farmed grouse from the sky and exposing his young children to hunting," one person tweeted. "I can't reconcile this with what he is saying."