Last night, Joan's daughter Melissa confirmed that the star had passed away aged 81 while in a New York hospital, following a cardiac arrest during a routine throat operation last week.
Heartfelt messages have been pouring in for the iconic comedienne and Kelly - who co-hosted E! show Fashion Police with Joan - has penned a very touching tribute.
Writing on her Facebook page, Kelly said: "I'm completely heartbroken by the loss of my beloved Joan. 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 cross my face.
"Laughter is what she gave us and laughter is what she would want us to do in remembrance of her. Melissa and Cooper, my thoughts are with you and I love you both so much.
"Joan, thank you for taking me in and loving me as a daughter. I will miss you deeply and will always hear your voice in my head saying 'my darling get out there and be you!"
Kelly also posted a black and white picture of Joan on the social networking site and it bore the quote: "Yesterday is history, tomorrow is a mystery, today is God's gift, that's why we call it the present."
Alongside it, Kelly commented: "You were one of the best gifts life has ever given me!"
Joan was first admitted to hospital after suffering a heart attack during a throat operation on 29 August. Six days later, Melissa confirmed that her mother had been placed on a life support machine.
Joan leaves behind Melissa and grandson Cooper.
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