Griffin took to Twitter on Friday night to tell fans that her sister Joyce, 65, had died.
The funny lady, 56, wrote "My sister Joyce passed away peacefully last night Check out this beautiful moment," and shared a video of a hospital worker singing to frail Joyce, who is smiling in her hospital bed.
At the end of the video, Griffin included a photo of Joyce in a healthy, happy time with her dark hair and Kathy noted, "…now she's having a Mai Tai on the beach in heaven," along with a link to support the American Cancer Society.
A few months ago, Griffin shaved her head to show sympathy for her sister's brave cancer battle.
Griffin's brother Gary died of esophageal cancer in 2014 and another brother, Kenny, died years ago. The comedian was the youngest of five siblings.
Griffin hasn't said what form of cancer ended Joyce's life.
Earlier this year, the jokester caused a firestorm after she participated in a shocking photo shoot with a bloody fake beheaded Donald Trump face.
The backlash was so great that Griffin got fired from her longtime CNN New Year's gig with Anderson Cooper.
Although Griffin apologized for the stunt she said was a joke, even pal Cooper reportedly thought she was out of line.
But she's trying to jump start her career again by planning a comedy tour.
We pay for juicy info! Do you have a story for RadarOnline.com? Email us at email@example.com, or call us at (866) ON-RADAR (667-2327) any time, day or night.