Like so many others, Kelly Osbourne is mourning the death of her beloved friend and mentor Joan Rivers.

On Thursday, September 4, just hours after Rivers took her last breath, Kelly took to her personal Facebook page to honor the late actress and comedian.

“I’m completely heartbroken by the loss of my beloved Joan,” Kelly wrote. “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,” she added. “Laughter is what she gave us and laughter is what she would want us to do in remembrance of her.”

“Melissa and Cooper [Rivers’ children], 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!'”

This was the very first time I met @Joan_Rivers in 1991 when I was 6 years old! https://t.co/962t9HbgDS

— Kelly Osbourne (@KellyOsbourne) September 5, 2014

Osbourne had worked with Rivers on E!’s Fashion Police since 2010, and had an instant connection with her. Rivers revealed in February 2013 that the feelings were mutual and she thought of Osbourne as a surrogate daughter.

I love you with all my heart @Joan_Rivers my life will never be the same with out you! https://t.co/0kn2FFZDF9 pic.twitter.com/zQnXlwepXh

— Kelly Osbourne (@KellyOsbourne) September 4, 2014

“I adore her and I’m very protective of her. And it has been wonderful to watch her, she’s grown on our show, and she’s changed and grown and matured and figured out the business,” Rivers said. “Kelly not only asks [Melissa] advice but do you want to know what’s wonderful? She listens. Kelly is wonderful.”

On the day of Rivers’ death, Osbourne had to be hospitalized for a bad case of pneumonia, and shared a photo of herself in the hospital bed, via Instagram.