“Ooh, Ooh, Ooh, Mr. Kotter!”

If you watched TV in the '70s, you probably recognize that line.

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So it’s with some sadness that we pass along word that Ron Palillo, the actor who played Arnold Horshack on ABC-TV’s Welcome Back, Kotter, has died in Palm Beach Gardens, Fla.

The Palm Beach Post writes that a friend of Palillo’s, Stacy Sacco, says he passed away this morning. Palillo’s agent, Scott Stander, tells CNN that the cause of death may have been a heart attack. Palillo was 63.

As TV Guide has written, Horshack was the “lovable schnook” among the students — Sweathogs, as they were known on the show — at a fictional in New York City. He would give that trademark line — the “ooh, ooh, ooh!” — when he thought he knew an answer (which he inevitably would get wrong). In real life, People magazine wrote in 1977, Palillo was a star student who could do Shakespeare.

The ABC show’s main character, teacher Gabe Kotter, was played by Gabe Kaplan. The young actor who broke out to become a huge star was John Travolta, who played Vinnie Barbarino. The show’s theme song, Welcome Back, became a hit for singer/songwriter John Sebastian.

TMZ.com has helpfully tracked down a very short video clip of Palillo as Horshack doing the “ooh, ooh, ooh!”

Robert Hegyes, who played Juan Epstein on Kotter, died last January.

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Update at 2 p.m. ET. “Not A Mean Bone In Him”:

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