He told GB News: “Kate is very, very keen on nature and the outdoors. That is a very important theme in her life at the moment.”
The expert also added that the promotion of “young people” enjoying the outdoors was also a key message of the image – something that Kate has often been vocal about.
The Princess, who was diagnosed with cancer last year and revealed earlier this year that she was in remission, has shared the healing power that nature has had on her during her journey.
The mother-of-three said in the Spring instalment of a video series titled Mother Nature: “Over the past year, nature has been my sanctuary.”
As well as the release of the new picture, Kensington Palace also released a new video of George and his siblings, Princess Charlotte, 10, and Prince Louis, seven.
The video, which was captured at the same time as the photo, shows George, Charlotte and Louis laughing and playing together.
In one particularly amusing moment, George and Charlotte are seen carrying their younger brother – with all three of them heard giggling.