Deputy President Kgalema Motlanthe didn't say one word when a young woman falsely claimed he had fathered a child with her.
His private life has pretty much always been a closed book.
After years of whispers about his lover and his estranged wife, the 63-year-old has for the first time shed light on this part of his life.
In Kgalema Motlanthe, A Political Biography by Ebrahim Harvey, Motlanthe reveals the reason for the breakdown of his marriage and his pending divorce from Mapula Motlanthe, a beautiful woman he met on a train on July 3 1970.
A section of the biography about his time on Robben Island, titled Prison letters and a painful episode, tells how Motlanthe's wife fell pregnant by another man while he was serving time.
The newlyweds had a son, Kgomotso, but in 1976, soon after their marriage, Motlanthe was jailed.
Five years later, Mapula gave birth to a daughter, another man's child.
The book, expected to be launched at the University of the Witwatersrand on Wednesday, gives a glimpse of the pain this caused him, but also shows that Motlanthe was willing to understand why she had done that.
In 2008, Mo tlanthe was the country's president for seven months, after former head of state Thabo Mbeki was recalled by the ANC. During that period, a 24-year-old woman claimed to have been his mistress and to be pregnant with his child. It turned out that Motlanthe had never had any dealings with the woman.
The ANC's former secretary-general served time on Robben Island alongside former president Nelson Mandela between 1977 and 1987.
Motlanthe gave fellow inmates such as Bafana Sithole, his close friend Stan Nkosi and late struggle stalwart Harry Gwala credit for helping him cope with the news of his wife's pregnancy.
Writes Harvey: "They provided him with constant support throughout those days. Some of the older ANC prisoners argued that when men suffer such a fate at the hands of their wives, they need to try imagining what they would have done if their wives were imprisoned for 10 or more years and they were at home alone and lonely."
He adds: "Perhaps he also saw that the apartheid system jailing him for 10 years would have been a big factor in the marriage breaking down and may have been the main reason."
The biography tells the story of a relationship that started showing cracks a few years into Motlanthe's incarceration.
"From 1982, for a year, Mapula stopped visiting and corresponding. Kgalema had no idea why. He and his family tried in vain to find out.
"It eventually transpired that Mapula was having an affair with another man."
In a letter written to Mapula in April 1983, Motlanthe wrote: "Try and imagine how I feel when all my letters to you seem to be swallowed by a big hole which mockingly challenges me to fill it up."
The biography tells how letters were "highly valued on the island" and how Motlanthe "terribly" missed Mapula's visits.
After it had emerged that Mapula was pregnant and subsequently had given birth, Motlanthe accepted the newborn baby, Ntabiseng, as though she were his own.
In one of the letters from Robben Island, he wrote: "Tell her I wish her good health and that I love her no end."
Ntabiseng was told that Motlanthe was not her father only when she turned 21.
Saths Cooper, Motlanthe's fellow inmate and a clinical psychologist, told the author of the biography that the news of the pregnancy would have hit Motlanthe hard, "especially when the environment he was in was itself very tough".
Motlanthe continued with the marriage after his release from prison in 1987, and the couple were blessed with another child.
"That is probably why he's such a strong person and leader today. To come through both Robben Island and something like that takes a very special person," Cooper says in the book.
Motlanthe has for several years been separated from his wife and is currently living with his partner, businesswoman Gugu Mtshali.
The book leaves the reader believing that there is no bitterness or animosity between Motlanthe and his soon-to-be ex-wife, both having accepted that their feelings for each other had changed.
He filed for divorce two years ago, and the matter is pending.
Harvey writes that he opted for divorce "as a result of the fact that his feelings for her had eventually changed" .
Mapula seemed to agree with that notion. "When he came back, we did not really connect. We were together, but there was little connection," she says in the book.
About falling pregnant while her husband was in prison, she says: "I was young and so many things happened."