The comedian shared the news on Twitter late Tuesday night while also paying tribute to her mom, who was a celebrity in her own right thanks to her appearances on "My Life on the D-List," which ran for six seasons.
"My Mom, the one and only, Maggie Griffin, passed away today," wrote Kathy. "I am gutted. My best friend. I'm shaking. I won't ever be prepared. I'm so grateful you guys got to be part of her life. You knew her. You loved her. She knew it. Oh, and OF COURSE she went on St Patrick's Day."
She also shared a photo of the two of them enjoying a drink together poolside.
My Mom, the one and only, Maggie Griffin, passed away today. I am gutted. My best friend. I'm shaking. I won't ever be prepared. I'm so grateful you guys got to be part of her life. You knew her. You loved her. She knew it. Oh, and OF COURSE she went on St Patrick's Day. 💔💔💔 pic.twitter.com/l9IZHuIWLb
"Maggie Griffin Godspeed," tweeted Sharon Stone, "So sorry @kathygriffin for your loss."
Jesse Tyler Ferguson sent "tons of love" Kathy's way, while Traci Lords tweeted, "Oh honey. I'm so sorry to hear this. Sending you and your family much love."
Kris Jenner commented on Instagram, writing, "God Bless precious Maggie and may she Rest In Peace ... love you Kathy." Ross Mathews added, "Oh Kathy. There are no words. What a beautiful relationship the two of you share. I wish that connection for everyone. I feel so lucky that I got to meet her. Thank you for sharing her with us all so we could love her even slightly as much as you do. I love you."
Selma Blair wrote, "Oh Kathy! I am so sorry. So sorry. She was always making me laugh when I watched you two. This grief will be deep. And hard. I am sure. Feel it. It will lessen. And she will be in every bottle of white you open. And everywhere else you find her spirit ... sending strength. And massive hugs."
Added Maria Shriver, "I'm so so sorry Kathy i know losing ones mother is one of life's hardest blows no pain like it i know May you be gentle with yourself may you know you have love around you and know i send you my love."
Jack Black left a blue heart emoji, before Gloria Estefan left a lengthy comment.
"I'm so deeply sorry, Kathy! Your mom was a very special human being and the bond you two shared was one of a kind" she wrote. "You are blessed to have had her for so long and she was blessed to have had you. The pain will be deep and strong but only because there was so much love, sharing and commitment. And the mere fact that she went on St. Patrick's Day is her parting message to you. Keep your heart open because I'm certain that she will continue to send messages that will give you peace in the knowledge that she's still with you, loving and protecting. May she Rest In Peace and you feel the satisfaction of knowing that you loved her well and took care of her always."
In January 2019, Griffin revealed her mother was suffering from dementia, sharing how hard it was to see Maggie's "so naturally quick, funny and smart" mind "slip away."
"In terms of how she is now, at this point she only knows my name and I love you," she shared at the time. "She loved making people happy and making people laugh. And trust me, I know she was the bigger star ... thank you from the bottom of my heart for giving us a lifetime of memories."
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