The comedian and TV presenter has passed away at the age of 67 and HELLO! understand that the royal is said to be "deeply saddened" by the loss.
The pair had worked closely together to support the work of Battersea Dogs and Cats home. Camilla will miss his "warm heart and infectious humour" which "lit up the lives of so many".
The royal family’s official Twitter account also paid tribute to the star, saying: "Deeply saddened to hear of the death of Paul O'Grady, who worked closely with Her Majesty in support of @Battersea_, providing lots of laughter and many waggy-tailed memories."
Paul died "unexpectedly but peacefully" on Tuesday evening, his husband Andre Portasio said in a statement.
"It is with great sadness that I inform you that Paul has passed away unexpectedly but peacefully yesterday evening," Mr Portasio said. "He will be greatly missed by his loved ones, friends, family, animals and all those who enjoyed his humour, wit and compassion.
"I know that he would want me to thank you for all the love you have shown him over the years."
Paul rose to fame in the 1990s with his iconic scouse drag queen persona Lily Savage, going on to present game show Blankety Blank and other light entertainment programmes.
Later in his career, he went on to host a number of chat shows, and also brought his love of dogs to the screen. And it was through the latter that he became close to Camilla.
Paul and Camilla bonded over their love of animals – in particular, dogs. The royal is the patron of Battersea Dogs and Cats Home, and previouly appeared on Paul O'Grady: For The Love of Dogs.
Speaking previously about their unlikely friendship, Paul said: "Camilla's a really funny woman — you can have a great laugh with her and you don't feel like you're on ceremony. I always get a big hug and kiss from her, too, which always shocks everybody."
Announcing her appearance on his TV show, Paul said at the time: "A lovely lady who's passionate about dogs. There was a competition to see whose dog would run straight to their owner ignoring the food, squeaky toys etc put in their way.
"The Duchess's dog ran straight to her, ignoring the temptation put in her way whilst Sausage [Paul's dog] headed straight for the press and photographers not a bit interested in the competition. She was obviously more interested in raising her profile and posing for the paps. A great day and the episode will be out later this year."
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