She was the “most beautiful woman in Puppetland” in the 1980s children’s show starring Paul Reubens, and more recently had a recurring role in “It’s Always Sunny in Philadelphia.”

A rep for the actress told USA TODAY a tumor was found in December near her liver and she died "a month or so after her diagnosis."

Lynne Marie Stewart, who is known as Miss Yvonne on Pee-wee’s Playhouse and Bonnie Kelly on It’s Always Sunny in Philadelphia, died Friday. She was 78. The cause of death has not been disclosed.