"A part of me is gone with his passing," Mlangeni said in an emotional goodbye today, during which he admitted that South Africa had not delivered on the expectations created by Mandela's life and legacy.
Sentenced to life imprisonment in 1964 at the same treason trial as Mandela, Mlangeni served 18 years of 26 years in the cell on Robben Island next to the man he knew as Madiba.
He is now only one of three surviving co-defendants of the landmark treason case that became known as the Rivonia trial, in which 10 African National Congress (ANC) leaders were tried for on charges of sabotage, public violence and bombings.
Mandela spent one more year behind bars than Mlangeni, finally emerging to lead his country into the modern post-apartheid era.
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"A great giant who strode the universe like a colossus is no more," Mlangeni said.
Mlangeni, who became a ruling African National Congress (ANC) MP in South Africa's first democratic elections in 1994, questioned whether the government had succeeded in the delivering the new life South Africans had been promised.
"We have done a lot, more than any other government has ever done," he said.
"But we have not done everything. There's still a lot to be done, a lot."
Income inequality between black and white citizens is stark, and by some measures is worse than it was at the end of apartheid.
Labour strikes and violent protests over services are an almost daily occurrence, attacks on migrants from elsewhere in Africa all too common
"We are saying to the leadership of the ANC, we know it's not easy, but let us try to do what Madiba has taught us to do," Mlangeni said.