South Africa's President Thabo Mbeki remains an "Aids dissident" - doubting the link between the HIV virus and Aids, according to his new biographer.
President Mbeki has long questioned orthodox views on HIV
Mark Gevisser told the BBC Mr Mbeki thinks he has "failed on the issue of Aids" and regrets dropping the debate.
He said Mr Mbeki believes anti-Aids drugs, now distributed in South Africa, are toxic and doubts their efficacy.
But the president's spokesman refused to comment on the book's claims, saying the cabinet and Mr Mbeki were united.
"The most important issue is that the government has a comprehensive HIV/Aids programme - described by UNAids as one of the most comprehensive in the world - and it has the support of the entire cabinet and Mr Mbeki," presidential spokesman Mukoni Ratshitanga told BBC News.
About 12% of South Africa's population is living with HIV, the virus most scientists believe causes Aids.
Mr Gevisser says the title of his book, Thabo Mbeki: The Dream Deferred, which is being launched in South Africa, explores what it is like for a man to come to power seeking to "bring salvation to your people".
But his dream becomes deferred for several reasons - one being globalisation that affected economic policies, he says.
"Another being that as you take hold of the reins of power you are told that the people you have just liberated are all suffering and dying from this epidemic caused by a virus that you can't even see and can't do very much about," Mr Gevisser told the BBC's Network Africa programme.
The biographer explained that Mr Mbeki has never doubted that there was an Aids epidemic, but "from the reading he had done that it was unclear what the cause of the Aids epidemic was".
"He feels even more strongly about the efficacy of anti-retroviral (ARV) medication. He believes that ARV medication is toxic and that it is a project that's been imposed upon particularly vulnerable Africans by the pharmaceutical companies," Mr Gevisser said.
But he said that Mr Mbeki was persuaded by colleagues to withdraw from the debate in 2002 because there was such a backlash to his position, something the president now "profoundly regrets".
Two years later, ahead of elections, the government revised its HIV policy and began distributing anti-retroviral drugs.
Some 380,000 patients are now on ARVs, although some 1.2 million are not receiving treatment.
According to UK newspaper The Guardian, Mr Mbeki recently called Mr Gevisser to specifically discuss Aids and sent a 100-page document explaining his views.
The document, received in June, describes the science of Aids as being entrenched in racist beliefs about Africans.
"There is no question as to the message Thabo Mbeki was delivering to me along with this document: he was now, as he had been since 1999, an Aids dissident," Mr Gevisser writes in his book.
South African Health Minister Manto Tshabalala-Msimang still comes in for criticism by Aids activists for sharing Mr Mbeki's views.
She has been nicknamed "Dr Beetroot" after recommending olive oil, lemon, beetroot and the African potato as elements of a healthy diet that could treat the symptoms associated with Aids.