(Photo credit: Kensington Palace)

Before Prince William and Duchess Catherine welcomed their son George, their main focus was their cocker spaniel, Lupo .

No longer.

Royal Baby Photos: First Official Images of Prince George

On Monday, it was Middleton's brother James who took over dog-sitting duty. James, 26, was photographed walking the dog through London. But why? Perhaps it's to help lighten the load for the Duke and Duchess. Or - worst case scenario - it's possible that the Windsors' canine child is not getting along with their human baby.

"When you have a young couple, like the royal couple, before they have children, the dog becomes the center of their universe. They treat it like their child," Nicholas Dodman, director of the Animal Behavior Center at Tufts University's Cummings School of Veterinary Medicine in North Grafton, Mass., told GoodMorningAmerica.com . "You can see how the dog becomes the center of their universe, totally spoiled, but that sets the stage for him having his nose get out of joint when their baby comes and disrupts his harmony."

(Photo credit: FameFlynetUK/FameFlynet Pictures)