Charles is well known for his love of surreal British comedy such as The Goons and Monty Python, which seems a little at odds with the acerbic wit of Rivers.
But the Prince and Duchess of Cornwall loved the American comedienne's near-the-knuckle humour and her larger-than-life personality.
And the feeling was mutual, with the US chat show host a very vocal supporter of the royal couple.
It was not until the comic was about 70 that she was reportedly introduced to Charles by a mutual friend while on holiday in the south of France in 2003.
The friendship quickly developed and she was invited to the Prince's wedding two years later.
A few months before the royal couple married, Rivers appeared on the Larry King show, praising Charles and Camilla's relationship:
"They are so right together. They are so terrific together and they complement each other. This should have happened 35 years ago."
The celebrity publicly expressed her admiration for them by doing what she did best - stand-up.
She was among a host of comics, from Robin Williams and John Cleese to Omid Djalili and Bill Bailey, who went on stage to entertain the Prince and Duchess and an audience of hundreds to mark Charles's 60th birthday in 2008.
Rivers was the most risque act of the night, telling the audience that sex is better when you are older because "we don't have to change our sheets - the nurses do it for us".
And two years ago she was on the bill at the Prince's Trust annual comedy gala attended by Charles and Camilla.
Rivers died in New York on Thursday. She had been in hospital since August 28, when she reportedly stopped breathing during a medical procedure on her vocal cords.
Charles is known for his love of comedians such as Spike Milligan and Robin Williams, who died last month in a suspected suicide.
10 of Joan Rivers's Sharpest One-liners
"I blame my mother for my poor sex life. All she told me was 'The man goes on top and the woman underneath'. For three years my husband and I slept in bunk beds."
"I don't exercise. If God had wanted me to bend over, he would have put diamonds on the floor."
"People say that money is not the key to happiness, but I always figured if you have enough money, you can have a key made."
"I've had so much plastic surgery, when I die, they will donate my body to Tupperware."
"I am definitely going to watch the Emmys this year! My make-up team is nominated for best special effects."'
"When a man has a birthday, he takes a day off. When a woman has a birthday, she takes at least three years off."
"You know why I feel older? I went to buy sexy underwear and they automatically gift wrapped it."
"At my age, an affair of the heart is a bypass."
"Boy George is all England needs - another queen who can't dress."
"My daughter and I are very close, we speak every single day and I call her every day and I say the same thing, 'Pick up, I know you're there'."
