In a foreword of a new book containing the memoirs of author Fatima Meer, Madikizela-Mandela wrote how she had been called urgently by her husband to Victor Verster Prison in 1988.
The former South African President had been moved there from Robben Island as the minority white apartheid government of F W De Klerk prepared the country for his release after 27 years as a political prisoner.
"On that occasion (Mandela) said he wanted to see Fatima to ask her to write his biography, 'Higher Than Hope'," Madikizela-Mandela recalled.
Fatima had followed Madiba's (Mandela's clan name by which he is affectionately known) instructions to be "brutally honest and had researched Madiba's private life and his numerous indiscretions", she wrote.
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OR was furious and demanded that all the chapters dealing with this be expunged, she wrote.
"Fatima and I did just that, but she later told me she kept those pages somewhere in a vault in the bank," Madikizela-Mandela said.
Madikizela-Mandela explained how the two families had been very close for decades, from the time that she first met Mandela while she was a junior social work student.
"Both Fatima and Ismail (her husband) were part of the core of the ANC that defied the segregational ideology of the oppressive regime of the time that forced our organisation to be splintered into the Indian Congress, the Congress of the Democrats, the Coloured (mixed-race) People's Congress and the African National Congress," she said.
"Fatima was born before her time. She was passionate about human rights, she was a sociologist and a born worker," Madikizela-Mandela wrote.