The Walk On By singer, who voiced the character Chef on the cult series, quit via a letter in March, 2006, but his son, Isaac Hayes III, insists his dad wasn't ready to walk away.

He tells The Hollywood Reporter his dad's resignation came after South Park's infamous 2005 episode Trapped in the Closet, in which an animated Tom Cruise is depicted hiding in a closet, refusing to get out, and Scientology is heavily mocked.

But Hayes, who governs his dad's estate, says, "Isaac Hayes did not quit South Park; someone quit South Park for him.

"What happened was that in January 2006 my dad had a stroke and lost the ability to speak. He really didn't have that much comprehension, and he had to relearn to play the piano and a lot of different things. He was in no position to resign under his own knowledge.

"At the time, everybody around my father was involved in Scientology - his assistants, the core group of people. So someone quit South Park on Isaac Hayes' behalf. We don't know who."

South Park creator Matt Stone admits he never really thought Hayes wanted to quit the show: "We sort of figured out the whole picture a bit later, but that's totally what happened... It really sucked, the whole thing. This statement put out that he was quitting, it kind of called us bigots."

Co-creator Trey Parker adds, "We knew in our hearts there was something way more rotten going on."

Hayes died in August, 2008.