The news of Stewart's death was confirmed Friday night in social media posts memorializing her life. TVLine has reached out to her reps for confirmation.
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"My heart is breaking upon hearing the news of my dear friend Lynne Stewart's passing," actress Cassandra "Elvira" Peterson wrote on Instagram Friday. "One of the kindest, sweetest, funniest women who ever lived."
Stewart is best known for playing Miss Yvonne on CBS' Pee-wee's Playhouse from 1986-1990. Her character's obsession with beauty, glamour and flirtation earned her the title of "The Most Beautiful Woman in Puppetland."
SNL alum Laraine Newman also paid tribute to Stewart on Instagram: "The most beautiful girl in Puppetland has left us. Lynne Stewart was truly an angel and brilliantly funny and an important part of our Groundlings family. As my sister said, 'If you don't love Lynne, you're just wrong.'"
During her decades-long career, Stewart appeared in other TV series including Comedy Bang! Bang!, 2 Broke Girls, Clinical Trials, Curb Your Enthusiasm, Grey's Anatomy, Son of the Beach, Nightstand, Superman, A Pup Named Scooby-Doo, Laverne & Shirley, Husbands, Wives & Lovers and M*A*S*H*.
Stewart most recently played Bonnie Kelly, Charlie's mom, in FX's It's Always Sunny in Philadelphia.