Kelly Osbourne posted a heartfelt tribute on Facebook
"Not only was she my boss, she was and will always be my teacher, therapist, closest friend, inspiration and the only grandmother I ever knew. She was family and I will never forget her.
"Laughter will be difficult for a while, but when I'm sad, lonely or upset all I will have to do is think of Joan and a smile will come across my face. Laughter is what she gave us and laughter is what she would want us to do in remembrance of her," she said, before paying tribute to Joan's daughter Melissa and her grandson Cooper.
Giuliana also mourned Joan's passing with a poignant message. "It is impossible to describe how much I adored Joan and how much she has meant to me.
The Fashion Police: Kelly Osbourne, George Kotsiopoulos, Joan Rivers and Giuliana Rancic
"She was not only the funniest woman I have ever met but was incredibly loving, honest and lived her life with no regrets. Working with her for the last 13 years have been one of the true joys of my life. She could put a smile on your face, instantly, no matter how hard your day was."
George, meanwhile, simply tweeted, "Rest in peace @Joan_Rivers. Thank you for changing my life. I will miss you so much."