In a rare personal statement, William and Catherine wrote: "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."
They signed off the message with a simple, "W & C".
The family are no doubt devastated by the loss.
Back in 2014, Lupo appeared in one of the first family portraits of William and Kate when they welcomed Prince George.
Snapped in a beautiful green field, the pup and baby made a family of four for the young couple.
Kate's brother, James Middleton is a known dog lover, and penned his own tribute to the pup whom he was close to given he was in the same family as James' own dogs.
"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. He was 9 years old."
He wrote of a dogs incredible ability to empathise and emotionally connect with a human, providing support where its needed.
"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."
James continued: "Many people over the years have reached out to me about the pain of loosing a dog and for most, the loss of a dog is, in almost every way comparable to the loss of a Human loved one.
"The pain I felt from loosing my first dog Tilly back in 2017 still hurts and on hearing the news about Lupo brought a wave of emotions flooding back."
He concluded by writing about how he lamented the loss of Lupo.
"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.
"Rest in peace Lupo. Tilly & Mini will be waiting for you. You will always be remembered and your legacy will live on forever. Good Boy."
This article originally appeared on our sister site Now To Love
