Butterflies are a firm favourite in the Cambridge household as Prince George, 8, celebrated his 1st birthday with a visit to the Sensational Butterflies exhibition at London's Natural History Museum in 2014.
Prince William - who also has Prince Louis, 3, with Catherine - previously admitted he felt a "new sense of purpose" in protecting the planet since having children.
The 39-year-old royal has "always loved nature" but his young family gave him added drive to do what he can to look after the natural world for future generations.
Speaking on the documentary "Prince William: A Planet For Us All" last year, he said: "Now I have got George, Charlotte and now Louis in my life - your outlook does change. You want to hand over to the next generation, the wildlife in a much better condition.
"I always believe it is possible to give young people hope and belief that things can get fixed.
"I have the belief that if we all work together, we can make a difference."
William's grandfather, the late Duke of Edinburgh, committed much of his life to helping to tackle environmental causes and promoting conservation.
Prince Philip - who died in April aged 99 - was the president of WWF-UK between 1961 and 1982, and president emeritus of WWF International.
And his grandson has continued Philip's efforts, launching the £50 million Earthshot Prize last year, which will be awarded annually from 2021 to 2030, to "five winners whose solutions substantially help the environment".
