Mr Mandela was speaking at a press conference hastily arranged at the headquarters of the African National Congress to honour the man who, when every other leader was in jail, held the organisation together and built it, from exile, into the most powerful political force in South Africa. That, Mr Mandela said, was the measure of Mr Tambo's achievement.
'I will feel his loss in a unique manner,' Mr Mandela said. 'We are bleeding from the invisible wounds that are so difficult to heal.' Coming just two weeks after the assassination of Chris Hani, the pain of Mr Tambo's death - he suffered a severe stroke at 3.10 yesterday morning - was written all over Mr Mandela's face.
The pair met at Fort Hare University in the Thirties, founded the ANC Youth League in the Forties and in effect took over the leadership of the organisation as a whole in the Fifties. With Walter Sisulu, they transformed the ANC from a passive to a militant revolutionary organisation constantly in conflict with the apartheid state. Mr Mandela and Mr Tambo also found time in the Fifties to establish South Africa's first black legal partnership.
In 1960 Mr Tambo, then deputy president of the ANC, was instructed by the organisation to go into exile. The feeling - quite correctly, as it proved - was that a dangerous new phase was beginning in the apartheid struggle, which could lead to the imprisonment and death of the ANC's top leaders. One of them had to leave the country to mobilise international support against apartheid.
Within five years, virtually the entire ANC leadership had been mopped up by the police, and it was left to Mr Tambo to keep the flame flickering. As president of the ANC, a function he officially assumed in 1969, he kept open lines of communication with the internal resistance, oversaw the development of the ANC's armed wing Umkhonto we Sizwe (Spear of the Nation) and, by the late Eighties, had outdone the South African government in the number of diplomatic missions the ANC had abroad.
In many countries he was received with the protocol usually afforded to heads of state. The family home was always London, but he himself spent most of his time either at ANC headquarters in Lusaka or travelling indefatigably around the globe.
One point he made over and over again was that the ANC had turned to war not out of bloodlust or revenge, but because the South African government had shut the door to negotiation. 'The need for us to take up arms will never transform us into prisoners of the idea of violence,' he declared in 1987. Three years later, after President De Klerk's decision to unban the ANC, he applauded the leadership's decision to abandon the armed struggle.
His final contribution before suffering a debilitating stroke in 1989 was to preside over the drafting of the Harare Declaration, a document fixing the ANC on the path to a negotiated settlement of the South African dilemma.
After a 30-year exile, he returned to South Africa to a tumultuous welcome in December 1990 and settled in the country six months later. At a national ANC conference in July 1991, Mr Tambo ceded the presidency of the organisation to Mr Mandela. Unlike Mr Hani, Mr Tambo was not able to sustain the myth that had built up around him. The stroke had left him partly immobilised on his right side and he walked with difficulty. He became the grandfather of the ANC, filling the largely honorary title of 'national chairman'.
But he was not inactive. Mr Mandela said yesterday that he had to be restrained, almost forcibly, from working a full five-day week. Right up to his death, he was working three days a week and, in Mr Mandela's absence, he would chair the meetings of the ANC's top leadership body, the National Executive Committee. He spoke softly, NEC members said yesterday, but always lucidly and with conviction, displaying in his later years the same qualities of gentle persuasion, the same instinct for compromise and consensus, which had provided the foundation of the ANC edifice during years of exile.
Mr Tambo's death at the age of 75 - he was nearly a year older than Mr Mandela - will not provoke anything like the outpouring of energy generated by Mr Hani's death. Partly because his death was entirely natural - though perhaps accelerated, ANC officials said, by the loss of Mr Hani - and partly because his ill- health meant he remained a remote figure for the majority of South Africans.
Those who worked under him in exile, however, have always been unanimous in their devotion to him. Where Mr Mandela inspires admiration, even awe, Mr Tambo inspired love.
Some criticism was heard after the Tambos moved into a pink- walled mansion in Sandhurst, one of Johannesburg's most expensive suburbs, but whatever rebukes there were have been levelled at Mr Tambo's formidable wife, Adelaide. It is a measure of the man that he himself rose above such mundanities. Though a devoted father, his concern centred more on the broader South African family, to which he devoted his life.