He was with them for nine years and was just a playful puppy when their first child, Prince George, was born.
Now Lupo – the adorable black cocker spaniel belonging to the Duke and Duchess of Cambridge – has passed on.
The devastated couple announced the news on their social media pages 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,” they wrote alongside a photo of their pet.
Kate’s brother, James Middleton, an avid dog lover with his own menagerie of spaniels, also shared a touching tribute.
“Nothing can prepare you for a loss of a dog,” he wrote. “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.”
Lupo has already been immortalised in the literary sense.
He was the subject of a range of children’ books by British writer Aby King about – you guessed it – the adventures of a royal mutt.
The 38-year-old mom and blogger offered her condolences to the Cambridges on Instagram. “I am deeply saddened since I owed so much of my own happiness to him. Lupo inspired me to write so many adventures for children.
Thanks to him I found a new way to bring the magic of the royal palaces to children. He lives on in my books and in future adventures I shall write with him. What a frightfully clever soul he was – rest in peace dear friend and thank you for changing my life forever.”
Sources: Instagram, people.com, dailymail.co.uk