In his new book 'External Mission: The ANC in Exile, 1960-1990', Professor Stephen Ellis, has unearthed fresh evidence that during his early years as an activist, Mandela did hold senior rank in the South African Communist Party, or SACP.
The former South African president now 94-years-old, who won the Nobel Peace Prize in 1993, has always denied being a member of the South African branch of the movement, which mounted an armed campaign of guerrilla resistance along with the African National Congress (ANC).
According to Ellis, Mandela joined the SACP to enlist the help of the Communist superpowers for the ANC's campaign of armed resistance to white rule, the Daily Telegraph reported.
As evidence of Mandela's Communist party membership, Ellis cites minutes from a secret 1982 SACP meeting, discovered in a collection of private papers at the University of Cape Town, in which a veteran former party member, the late John Pule Motshabi, talks about how Mandela was a party member some two decades before.
In the minutes, Motshabi, is quoted as saying: "There was an accusation that we opposed allowing Nelson (Mandela) and Walter (Sisulu, a fellow activist) into the Family (a code word for the party) ... We were not informed because this was arising after the 1950 campaigns (a series of street protests).
The recruitment of the two came after."
The minutes from the 1982 SACP meeting, said Ellis, offered more reliable proof. "This is written in a closed party meeting so nobody is trying to impress or mislead the public," Ellis said.
On Friday night, a spokesman for the Nelson Mandela Foundation said: "We do not believe that there is proof that Madiba (Mandela's clan name) was a Party member ... The evidence that has been identified is comparatively weak in relation to the evidence against, not least Madiba's consistent denial of the fact over nearly 50 years".
During the Rivonia trial, when Mandela and nine other ANC leaders were tried for 221 alleged acts of sabotage designed to overthrow the apartheid system, the anti-apartheid icon had declared that he had "never been a member of the Communist Party," and that he disagreed with the movement's contempt for Western-style parliamentary democracy.
"He knew and trusted many Communist activists anyway, so it appears he was co-opted straight to the central committee with no probation required," Ellis said.
"But it's fair to say he wasn't a real convert, it was just an opportunist thing," he added.