'Mandela's Last Years' was written by the Nobel laureate's doctor of almost 10 years -- Vejay Ramlakan.
Ramlakan, a former South African military doctor who was Mandela's physician during the last months of his life, has claimed that he received permission for the book from the Mandela family but refused to say who exactly authorised him.
Mandela family spokesman Mandla Mandela and Mandela's widow Graca Machel are taking legal advice, saying they had not granted the permission.
"We believe that the book shouldn't have been published in the first place, at least from the things that we have thus far been able to find that are just inaccurate in the book," the Nelson Mandela Foundation's chief executive Sello Hatang told TV station enews yesterday.
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The executors of Mandela's estate said that the content of the book was "deeply regrettable and unfortunate and constitute unlawful disclosures".
The executors have decided to take remedial steps.
The executors include former chief justice of South Africa Dikgang Moseneke and advocate George Bizos, who was part of the defence team at the infamous trial of Mandela and others that sent them to Robben Island for decades.
Random House said it had accepted 'Mandela's Last Years' for publication after Ramlakan advised it that he had been asked by a Mandela family member to publish the book.