Kate Middleton and Prince William with their dog Lupo at Beaufort Polo Club in Westonbirt, Gloucestershire on June 17, 2012. Credit: Alpha/Landov

Prince William's paternal instincts are showing through!

On Sunday, England's future king, whose 30th birthday is later this week, was among the players at a charity polo event in Gloucestershire, England. His wife Kate Middleton and brother Prince Harry were also on hand for the Gloucestershire Festival of Polo, at the Beaufort Polo Club (benefitting various children's charities), but William's fave buddy at the bash was definitely Lupo -- the cute cocker spaniel puppy he and the Duchess, 30, adopted earlier this year.

After dismounting from his steed, William eagerly picked up Lupo, who is about six months old, and showered him with sweet kisses.

The Duchess, slim and stunning in a pair of tight jeans, button downshirt and leather jacket, was also photographed at the event with pal Autumn Phillips and her adorable young daughter Savannah Phillips.

If all goes as planned, the spouses of one year will soon have their own (human!) baby to fawn over.

"There's a window in place," a royal insider confirms in the new Us Weekly of the couple's plan to conceive. Another insider explains that the Duke and Duchess hope to conceive their first child anytime between the last leg of their royal tour in September 2012 and summer 2013.

Their ideal? A New Year's announcement! Once Middleton hits the three-month mark in her pregnancy, "the pregnancy will be announced," says the insider. "It won't be hidden."

Kate dished on her romantic hubby to 28 youngsters during a camping trip Sunday. "I am very well looked after," she said. "William is very sweet and kind of spoils me."