Bongiwe Gloria Ngema, who recently accompanied Mr Zuma on a state visit to China, is expecting a child early next year, according to media reports citing her close friends. The pair already have one child and are due to marry in December, which will bring to four the number of South Africa's First Ladies.
Reports of the pregnancy comes only a fortnight after the arrival of Mr Zuma's 21st child, which was born to the second of his current wives.
The boy, named Manqoba Kholwani which means "believe it", arrived amid claims that he could be the result of an affair between his mother and her bodyguard. The president has dismissed the claims as malicious rumours.
Now aged 68, Mr Zuma has faced repeated calls to live a quieter life and devote more of his energies to leading his country out of the griding poverty which confronts the majority of the population.
Mr Zuma's advisers insist that, as a proud Zulu, his culture permits him to have as many children as he wants with as many partners as he likes. However, the president was forced to make a humiliating apology earlier this year following the birth, out of wedlock, of his 20th child to the daughter of a family friend.
While polygamy is accepted in South Africa, the spiralling cost to the taxpayer of Mr Zuma's cultural observance has led to bitter clashes between the president's ruling African National Congress and the leading opposition party. News of yet another child and another marriage is bound to reignite the debate.
Taxpayers are already spending more than £1.3m a year to support Mr Zuma's current wives and some of his children. Generous friends are also known to help "sponsor" additional costs which do not have to be declared in public.
The "presidential spousal budget", which had doubled in the space of a year, was condemned as "exorbitant" by the opposition leader, Helen Zille. This prompted a sharp riposte from the ANC which accused Ms Zille, who is white, of "cultural intolerance".
The spousal office, which organises access to the president for his wives and fiancée, also pays for the women's personal support staff, such as secretaries and researchers, as well as domestic and international air travel and accommodation.
Mobile phones for the consorts and their secretaries, laptops and printers and a special daily allowance for "incidental" expenses are also covered.
"It is impossible for anyone, even on a president's salary, to look after a family of the size of Zuma's without relying extensively on private benefactors and the taxpayers' money," Mrs Zille said.
