The couple used the modern medium of Instagram to inform their followers of the Royal death. “Very sadly last weekend our dear dog, Lupo, passed away,” the couple wrote. “He has been at the heart of our family for the past nine years and we will miss him so much.” They signed off the message with a very personal “W & C”, short for William and Catherine, and accompanied the statement with a photograph of Lupo, looking frankly just a little bit regal, lying down but his head held high. Lupo appears thoughtful, as if the future of the monarchy is dependent on him, although in reality, he was probably just wondering where his next dog biscuit was coming from.

Within an hour of the message being posted, it had garnered an astonishing 300,000 messages of support from wellwishers. Lupo had indeed touched hearts.

The spaniel had been a wedding present from the Duchess’s younger brother James Middleton, who said on Sunday that “nothing can ever prepare you for the loss of a dog”.

Lupo arrived in the Royal household in early 2012, just in time to keep the Duchess of Cambridge company, after Prince William had deployed for six weeks to the Falkland Islands while serving as an RAF search and rescue pilot. Lupo was key in helping her get through the time apart.

His name, at first, remained unknown, royal aides refusing to disclose it as a breach of privacy. The Duchess let it slip to primary school children on a classroom visit in February 2012. Within hours, Lupo had his own Twitter account. He also has his own Wikipedia entry while Hello! put him on the front cover. “Kate’s puppy love”, declared the magazine, announcing his arrival with the added strapline: “Introducing the gorgeous boy who’s put a spring in the step of the Duchess.”

Lupo was an ever-present thereafter, appearing in 2013 alongside a tiny Prince George, the Duchess cradling her baby son and the Duke with his arm around the panting, smiling dog. Prince William declared after the birth of their son: 'For me Catherine and now little George are my priorities”, before adding: “and Lupo.” The dog, he said, was taking a “little bit of time to adapt” to the baby but was doing just fine.

Reports suggest Lupo had a role to play in making history. Unsure what to call the future king, the Duke and Duchess had written a number of names on scraps of paper and invited Lupo to wander among them. He stopped when he reached the piece of paper with George written on it.

Other photo opportunities came Lupo’s way like in 2016, with Prince George knelt on a picnic rug clutching an ice cream, and the spaniel doing his best not to lick it. The incident sparked a warning from the RSPCA for owners not to feed their dogs dairy products.

Lupo was a family affair, his mother Ella being owned by Carole and Michael Middleton, the Duchess’s parents. Ella is still alive and Lupo (meaning wolf in Italian) has died at a relatively young age for a cocker spaniel. Kensington Palace declined to discuss the cause of death.

In a post on Instagram, James Middleton wrote of his sister’s devastation.

"It is with great sadness that Lupo, the beloved dog of my sister Catherine and her family has passed away. Lupo was the son of Ella, brother to Zulu, Inka & Luna,” wrote Mr Middleton.

"Nothing can ever prepare you for the loss of a dog. For those who have never had a dog, it might be hard to understand the loss. However those who have loved a dog know the truth: a dog is not just a pet; it is a member of the family, a best friend, a loyal companion, a teacher and a therapist.”

He said that the loss of a dog was “in almost every way comparable to the loss of a human loved one” and said the death of Lupo had “brought a wave of emotions flooding back” over the death of his own dog Tilly in 2017.

"There isn't much of a rule book on how to grieve for a dog,” posted Mr Middleton, “but I've said a prayer, lit a candle and taken Ella (Mum) for a long walk to spend time remembering Lupo.”