The nine-year-old black cocker spaniel was a wedding present from Kate’s brother James.

William and Kate said in an Instagram post on Sunday: “Very sadly last weekend our dear dog, Lupo, passed away.

“He has been at the heart of our family for the past nine years and we will miss him so much.”

Following the birth of Prince George in July 2013, William said Lupo had coped very well with the upheaval in the house.

“He’s coping all right, actually,” he said.

“As a lot of people know who have got dogs and bring a newborn back, they take a little bit of time to adapt, but, no he’s been all right so far.”

He added: “He’s been slobbering sort of around the house a bit, so he’s perfectly happy.”

In pictures taken to mark Prince George’s third birthday, the little royal caused controversy by offering Lupo a lick of his ice cream.

It prompted the RSPCA to warn people not to give dairy products to their dogs, as they can be toxic, although the animal welfare charity praised George for trying to help Lupo keep cool in the summer heat.

Spaniels, which were bred as gun dogs, are known for being high energy and Kate once wistfully commented on a charity worker’s well-behaved dogs on a visit to Keswick in the Lake District.

“Maybe we should lend you Lupo,” she joked.

As recently as March, Kate revealed table tennis was a difficult activity in their household because of Lupo’s determination to get involved.

-AAP