Terry Lubbock, the father of Stuart Lubbock, the man found dead in Michael Barrymore’s swimming pool in 2001, has died at the age of 76.
Mr Lubbock died after being diagnosed with terminal cancer, his friend and publicist Harry Cichy said.
He had mounted a 20-year campaign for justice for his son.
A post-mortem examination revealed that Stuart Lubbock, 31, had suffered severe internal injuries which suggested he had been sexually assaulted.
Alcohol, ecstasy, and cocaine were found in his bloodstream.
No one has been charged in relation to Stuart Lubbock’s death.
Terry Lubbock was a retired toolmaker from Harlow in Essex.
Mr Cichy said he died on 15 September and described him as “incredible”.
“You don’t come across many people like Terry Lubbock,” said Mr Cichy.
“His tenacity and determination were incredible. He looked like a mild-mannered man, but he had the heart of a lion.
“He thought about Stuart every waking hour, seven days a week.
“He’s died sad because he’s died knowing people never knew the truth about what happened. But no one could have fought harder for their son.”
Terry Lubbock, who was divorced and had another son, Kevin, was fighting for a fresh inquest into his son’s death.
“A new inquest was what really mattered to him,” said Mr Cichy.
“He had lost faith in the police.
“Sadly, he’s died not knowing whether there will be another inquest.”
In February, Terry Lubbock told journalists that he had terminal cancer and said doctors had told him he had months to live.
He made a “final appeal” for witnesses to come forward in April and said at the time: “We would like old witnesses to come forward and tell the truth.”
“For me, the clock is ticking, and time is running out. This will be my final appeal.”
Mr Barrymore, now 69, was arrested in 2007 but never charged with any offence.
He subsequently sued Essex Police, claiming his wrongful arrest had cost him about £2.5 million in lost earnings, but Court of Appeal judges concluded he should receive nominal damages.