Lynne Marie Stewart, a comedian and actress best known for appearing in Pee-wee’s Playhouse and It’s Always Sunny in Philadelphia, has died at 78, according to a report.

Stewart’s death was confirmed Friday to The Hollywood Reporter by a spokesperson for her former sketch troupe, the Groundlings. A cause of death was not disclosed.

An industry veteran, Stewart got her big break as Miss Yvonne (“the most beautiful woman in Puppet Land”) alongside Paul Reubens’ Pee-wee Herman, a role which she reprised throughout the 1980s. Stewart also portrayed Charlie Kenny’s mother on the long-running dark comedy series It’s Always Sunny.

She was a member of the Los Angeles-based troupe the Groundlings from the 1970s and 80s. “We are heartbroken to hear of the passing of our dear sweet Lynne Stewart,” the Groundlings wrote in a statement to THR.