Mandla Mandela was speaking at the funeral of his father, Makgatho, 54, Nelson's last surviving son.

Hours after Makgatho died in a Johannesburg hospital last week, Mandela announced that his son had died of Aids-related complications. Mandela said his announcement was a plea for everyone to be more open about the disease, which kills about 600 South Africans a day.

Yesterday, standing in the sunshine in a remote Eastern Cape field, Mandla Mandela told mourners his mother Zondi died of the same disease. The family had previously said she died of pneumonia - a euphemism for Aids in South Africa as one of a handful of diseases which kill once the HIV virus has destroyed the immune system.

'In spite of this, we are not used to death,' he said.

Among the 4,000 people at the funeral near Nelson Mandela's home were his former wife, Winnie Madikizela-Mandela, President Thabo Mbeki, Archbishop Desmond Tutu and local villagers.

A frail, gaunt-looking Nelson Mandela sat quietly next to his wife, Graça Machel, gazing at the brown coffin covered in white and yellow flowers. The 86-year-old wore a red Aids ribbon to symbolise the fight to which he now seems determined to dedicate the final years of his life.

The fact that Makgatho had Aids was announced by his father immediately after his death and the gesture towards openness was applauded around the world. It was seen as a blow against the stigma attached to the disease in South Africa, which makes the pandemic so difficult to combat.

Ironically, hospital sources have told The Observer Makgatho did not die of an Aids-related illness, but of a pancreatic cancer. He had been on anti-retrovirals for some time and his Aids was described as being 'well under control'. It would, however, have affected his body's capacity to fight the problem with his pancreas.

The fact that Makgatho had Aids was kept secret from Nelson until June last year. He apparently spent much time at his son's bedside, holding his hand.

Recently announcing his retirement from public life, he has now made an exception where Aids is concerned and has expressed regret that he failed to tackle the issue while President.

Makgatho Mandela was a tragic figure, variously characterised by those who knew him as 'intensely shy', 'introspective' and 'a dead soul'. A reformed alcoholic and a high-school drop-out he was one of four children born to Nelson by his first wife, Evelyn. One daughter died as a baby in 1948, another son in 1969. Makgatho was himself married twice. He had one child by his first marriage and three by his second.

He seemed to have suffered most from his father's imprisonment. Nelson used to complain about his failure to write letters. Makgatho's first wife, Reyne, filled the gap, maintaining a correspondence with her father-in-law, but she divorced her husband and married an Englishman.

The relationship between Evelyn's children and Winnie Mandela was particularly bad. Anthony Sampson, in his authorised biography of Nelson Mandela, quotes Makgatho's sister, Maki, as saying: 'We were at war with Winnie.' Anecdotes told about Winnie's treatment of Makgatho's son, Mandla, would suggest it was a feud that became generational.

On his release from prison, Nelson took his son in hand, insisting that he finish his schooling and do a law degree at Natal University. In his 40s, Makgatho seems to have become a driven student under his father's eye.

When it was noticed that he was not at Nelson's presidential inauguration he explained that he had an exam the following day. After graduating in 1997, he joined Standard Bank as a 'legal consultant'.

Makgatho was buried at the Mandela ancestral home at Qunu in the Transkei. It was a moment which brought to mind a heart-breaking passage in his autobiography, A Long Road to Freedom, describing how, in prison, he was told the news of the death of his eldest son, Thembi - Makgotho's brother - in a car accident.

'I returned to my cell and lay on my bed. I do not know how long I stayed there...' recalled Mandela. 'Finally Walter [Sisulu] came to me and knelt beside my bed and I handed him the telegram. He said nothing, but only held my hand. I do not know how long he remained with me.

'There is nothing one man can say to another at such a time.'

More than five million of South Africa's 45 million people are infected with HIV, more than in any other country. But until this year the government refused to provide life-prolonging anti-retroviral drugs through the public health system, citing concerns about their safety and cost.

It has now promised to provide free treatment to all who need it within five years.

Mandela has been an outspoken Aids campaigner, criticising the government for its slow reaction to combat the disease.