Ron Palillo, who played Horshack on Welcome Back Kotter, has died.

TMZ and WPTV in Palm Beach report that Palillo’s death was sudden and unexpected. He was found in his Palm Beach house by his partner of 41 years, Joseph Gramm, and was pronounced dead Tuesday morning.

A friend of Palillo’s, who calls him “fun and intelligent,” told WPTV that the actor’s cause of death had not been determined, but TMZ said he died of a heart attack.

Welcome Back Kotter, which aired on ABC from 1975-79, starred John Travolta and Gabe Kaplan and concerned itself with the wacky goings-on of the so-called Sweathogs in a remedial high school class.

After Kotter, Palillo guest-starred on numerous TV series, did voice roles and appeared on Broadway. He was also an artist, who provided the art for two children’s books, The Red Wings of Christmas and A Gift for the Contessa.

In 2005, The Lost Boy, a play that Palillo wrote about the life of Peter Pan author J.M. Barrie, premiered on Broadway.

Palillo had been working as a teacher at a school called the G-Star Academy in Palm Springs.

His is the second death of a Kotter cast member. Robert Hegyes, who played Juan Epstein on the show, died from a heart attack in January.