The Duke and Duchess of Cambridge have revealed that their beloved dog Lupo has died.

The nine-year-old black cocker spaniel was a wedding present from Kate’s brother James, who is thought to have bred him.

Prince 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.”

British tabloid the Telegraph reported Kensington Palace declined to discuss the dog’s cause of death.

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.”

Prince William with Lupo at the polo in 2012. Photo: Getty

Lupo featured in many of the Cambridges’ landmark photos – he was there in the first official photo of baby Prince George, and for the young royal’s first birthday.

In one picture marking Prince George’s third birthday, he was snapped by Kate offering Lupo a lick of his ice cream.

That 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.

James Middleton, Kate Middleton’s brother, who still has Lupo’s mother, also shared his grief for the dog.

“There isn’t much of a rule book on how to grieve for a dog, but I’ve said a prayer, lit a candle and taken Ella (mum) for a long walk to spend time remembering Lupo,” he wrote in an emotional Instagram post.

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.

-with AAP