Around noon on Thursday, Osbourne posted a photo of herself on Instagram looking under the weather and holding up a sign that says "Why I am in the hospital" with the caption, "When you have a cough go to the doctor or you will end up like me! #Pneumonia."
The photo was posted just before news broke of Rivers' passing and, within a couple hours, Osbourne had again taken to social media to remember the comedienne who served as her superior on Fashion Police.
Osbourne wrote a touching tribute to Rivers on Facebook. "I'm completely heartbroken by the loss of my beloved Joan," Osbourne wrote. "Not only was she my boss, she was and always will 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.'"
Osbourne also posted a link to Change.org on Twitter, petitioning to make Sept. 4 National Joan Rivers Day.
Rivers passed away on Thursday after going into cardiac arrest during a routine vocal cord procedure last week. She was revered by many for blazing the trail for women in comedy and was also extremely active in working for gay rights, as well as garnering attention for suicide.
Our thoughts are with Rivers' family and friends and we're sending best wishes to Osbourne for a speedy recovery.
And you'll see personalized content just for you whenever you click the My Feed .
SheKnows is making some changes!