Prince William and Kate Middleton mourn death of dog Lupo: 'He has been at the heart of our family'

The black cocker spaniel was a wedding present from the duchess's brother, James

The Duke and Duchess of Cambridge are mourning their pet dog, Lupo, who died aged 9. 

The Duke and Duchess of Cambridge have announced the death of their family dog, Lupo.

The 9-year-old black cocker spaniel died last weekend, the royal couple announced in an Instagram post.

"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," the couple wrote, signing the message off informally with "W & C", for William and Catherine.

The family dog was a present from the duchess's brother, James Middleton, following their April 2011 wedding.

Famously, he was present for the first photo the couple shared with a newborn Prince George from her parents' family garden in Bucklebury, England, in August 2013. Also present in the photo was a sleeping Tilly the retriever, the Middleton family pet.

Lupo has been in a number of past family photos, and was said to be very tolerant of the three Cambridge children running around the house.

Following the arrival of Prince George, Prince William said at an event: "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's been slobbering sort of around the house a bit, so he's perfectly happy."

James Middleton breeds the dogs, and often shares photos of the animals on his Instagram. He, too, penned a tribute to Lupo.

"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 and Luna," Middleton wrote, sharing a number of photos of the dog.

"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 for 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 continued.

"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 added. "Rest in peace Lupo ... You will always be remembered and your legacy will live on forever. Good Boy."