The subject — Grace Van Cutsem, the 3-year-old godchild of William, daughter of his good friend Hugh van Cutsem and a descendant of the Astor family — is a small child. Thus, she falls into the same recipe category as baby penguins or kittens. Plus, she's totally unselfconscious.
The internet immediately leaped on the photo like a litter of beagles on a hollow bone filled with peanut butter. But the best was Buzzfeed, for inviting readers to cut and paste the internet's newest face onto other images.