Nelson Mandela received rapturous applause as he unveiled a blue plaque at the former home of two eminent anti-apartheid activists in London.
Mr Mandela said the couple were 'great comrades'
Hundreds of people gathered outside 13 Lyme Street, Camden, north London, as the former South African President paid a personal tribute to Ruth First and her husband, Joe Slovo.
Mr Mandela said the couple, who lived there between 1966 and 1978, were "great comrades" who had helped to achieve a democratic society in South Africa.
The house was a meeting place for an international group of exiles and was a focus for activists involved in the changes in the whole of Africa.
Mr Mandela said: "It is a great honour to appear on this occasion because we are honouring two eminent South Africans who, as young people, decided to join forces against those who suppressed millions of people in our country."
Ruth First was killed by a parcel bomb
Also present was Camden MP Frank Dobson, who said: "This is a great day for Camden Town and for Camden where the British anti-apartheid movement was founded."
First met Slovo at university in Johannesburg.
The politically active couple were listed as communists under the Suppression of Communism Act of 1954 and could not attend public meetings or be quoted in the press.
They went into exile in 1963.
During the 12 years that they lived in Camden, First continued her campaign for freedom through writing while Slovo worked for the African National Congress (ANC).
Joe Slovo returned to South Africa in 1990
In 1982, First was killed by a parcel bomb, believed to have been sent by the apartheid regime in Mozambique, where she was teaching.
Slovo continued the fight for freedom and became the first white member of the ANC national executive council in 1985.
He was appointed general secretary of the South African Communist Party the following year.
When President F W De Klerk lifted the 30-year ban on the ANC in 1990, Slovo returned to South Africa.
He gained a seat through the ANC in South Africa's first multiracial elections in April 1994 and became Minster for Housing, a position he held until his death from leukaemia in January 1995.