South Africa's main opposition party has accused President Jacob Zuma of directly contradicting the government's message on the prevention of HIV and AIDS.
The Democratic Alliance issued a statement after the Sunday Times newspaper reported that Mr Zuma had fathered a child out of wedlock in October last year.
Earlier this year, Mr Zuma married for the fifth time and is thought to have at least 20 children.
The BBC reports there has been no comment from the woman, Sonono Khoza, Mr Zuma, or his party, the ANC.
Mr Zuma has always refused to say exactly how many offspring he has fathered.
Ms Khoza, aged 39, works for a bank. She has a famous father: Irvin Khoza is a friend of Mr Zuma and, as chairman of the World Cup Organising Committee, is one of the most powerful men in South African football.
The BBC reports Mr Zuma's private life is never far from the headlines.
In 2006, while being acquitted of rape, Mr Zuma admitted that he had made a mistake by having unprotected sex.
The Democratic Alliance said the latest accusations showed the president undermining the struggle against AIDS by having unprotected sex with multiple partners.
Polygamy is permitted in South African law and is regarded as an important part of Zulu culture.