Palillo was apparently found by his partner, Joseph Gramm, around 4:00 a.m. Palillo was rushed to a nearby hospital, where he was pronounced dead at 63 years old.

Palillo was best known for playing Arnold Dingfelder Horshack on Welcome Back, Kotter, but he did also appear on Ellen, Darkwing Duck, Laverne and Shirley in the Army and he appeared in Friday the 14th Part VI: Jason Lives.

In recent years, Palillo taught at G-Star School of the Arts for Motion Pictures and Broadcasting in Palm Beach County, Florida. He also produced his first full-length play, the Lost Boy, in 2005 and, in 2007, he introduced a clothing line spcializing in limited-edition t-shirts created by Rotter and Friends.

Earlier this year, "Kotter" co-star Robert Hegyes, who played Epstein, also passed away, also from a heart attack.

Rest in piece, Ron Palillo.

Source: 'Welcome Back, Kotter's' Horshack passes away