Announcing the news on Instagram, the couple posted a sweet photo of the black cocker spaniel with a touching caption.
“Very sadly last weekend our dear dog, Lupo, passed away,” it reads. “He has been at the heart of our family for the past nine years and we will miss him so much.”
Lupo was welcomed to the family in 2012, bred from Ella, the Duchess’ parents’ dog.
Over the years, Lupo has featured in many of the Cambridge’s family portraits and has even inspired a children’s book series, The Adventures of Lupo.
The Duchess’ brother, James Middleton, shared a moving message to Lupo on Instagram.
“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,” he wrote.
“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.”