Lynne Marie Stewart, the actress best known for her roles in “American Graffiti,”  “Pee-wee’s Playhouse” and “It’s Always Sunny in Philadelphia,” has died, according to a former Hollywood colleague.

Cassandra Peterson, known for her iconic “Elvira” character, shared the sad news on IG, writing … “My heart is breaking upon hearing the news of my dear friend Lynne Stewart’s passing. One of the kindest, sweetest, funniest women who ever lived. The iconic Miss Yvonne of Pee-wee’s Playhouse: She’ll always be ‘the most beautiful woman in Puppetland’. 💔”

Stewart was in CP’s “Elvira: Mistress of the Dark” … Cassandra and the late ‘Pee-wee’ actor Paul Reubens were super close, so stands to reason she’d know.

As Cassandra noted, Stewart played Miss Yvonne, The Most Beautiful Woman in Puppetland, on “Pee-wee’s Playhouse” from 1986 to 1990 … and she appeared in several other ‘Pee-wee’ titles, including “Pee-wee’s Big Adventure” and “Big Top Pee-wee.”

The actress also appeared in the iconic George Lucas film “American Graffiti” and the Arnold Schwarzenegger classic, “The Running Man.”

Stewart’s more recent fan-favorite role was as Charlie Kelly’s mother Bonnie, in “It’s Always Sunny in Philadelphia.”

She was 78.