Prince William had a special photo on display in a new video released on Friday. As the Duke of Cambridge typed away on a typewriter in the 15-second clip, a photo of Prince Philip and Prince George could be seen behind him.

The adorable picture of George and his paternal great-grandfather was released in April following the Duke of Edinburgh’s death. The photo was taken by the Duchess of Cambridge back in 2015 in Norfolk.

William was promoting the upcoming Earthshot: How to Save Our Planet book in the new video. “In my introduction to Earthshot: How to Save our Planet, the authoritative book of The @EarthshotPrize, I wanted to share the early conversations in 2018 that led to the Prize’s creation and the simple equation that captures my theory behind Earthshot: Urgency + Optimism = Action,” a message alongside the clip reads.

The book, co-written by Colin Butfield and Jonnie Hughes and featuring an introduction by the Duke of Cambridge, will be available in the UK on Sept. 30 and on Oct. 5 in North America. Earthshot: How to Save Our Planet has been described as a “book of action and optimism to save our planet.” Kensington Palace previously tweeted that it “aims to inspire a decade of action to repair our planet.”

The first Earthshot Prize Ceremony is scheduled to take place on Oct. 17 in London. Ahead of the ceremony, a new five-part series spotlighting the prestigious environment prize will be released on Discovery’s subscription streaming service: discovery+.