Duke is moved by threat to rhinos in Africa

William was left close to tears after being shown footage of a rhino attacked by poachers and left bleeding to death during filming for a documentary.

The royal was interviewed in July, soon after the birth of his son Prince George.

In the programme, to be screened by ITV and CNN on Sunday and Monday respectively, he talks about his passion for wildlife.

Documentary film maker Jane Treays, writing in the latest edition of the Radio Times, said that during the informal chat filmed at Kensington Palace William told her: “The wildlife is incredibly vulnerable and I feel a real protective instinct, more so now that I am a father, which is why I get emotional about it...you want to stand up for what is very vulnerable and needs protecting.

“Elephants, rhinos and many other animals that are persecuted don’t have a voice.”

Ms Treays wrote that William became emotional when shown footage of the rhino: “Tears well in his eyes and he confesses to everything being changed by the birth of his son.”

The Duke says in the documentary: “It’s just so powerful. You’d think something that big and that’s been around so long, would have worked out a way to avoid being caught and persecuted, but they really don’t. I do feel anger, but I also feel really great hope that we will overcome this as a human race.”

He said his family had inspired him to champion causes he believes in.

The Duke said: “The legacy is quite a daunting one, following on from my grandfather and father. It just sort of happened... My mother would come back with all these stories, full of excitement and passion for what she had been doing and I used to sit there, quite a surprised little boy, taking it all in - and the infectious enthusiasm and energy she had rubbed off on me.”

William’s interest in Africa’s natural world is reflected in his royal patronage of the UK-based African wildlife conservation charity Tusk Trust.

The Cambridges will attend the organisation’s inaugural awards ceremony in central London on Thursday night.

He added: “I want the awards to be credible in the conservation world and for those who receive them to realise how fantastic their work has been. They are leading the way. Now is the time to galvanise and energise all the people who want to help.”

Tusk Trust establishes and promotes community-driven conservation programmes in Africa.

Asked by Ms Treays about the legacy for Prince George he laughed: “At the moment, the only legacy I want to pass on to him is to sleep more and maybe not to have to change his nappy quite so many times, but as he gets older I’m sure he’ll pick up the bug of conservation.”