Former president FW De Klerk said South Africa lost one of its founding fathers and "greatest sons". He said Nelson Mandela made a "unique contribution" to constitutional democracy and nation-building.

"It was with the greatest sadness that I have learned of the death of Nelson Mandela. My wife, Elita, and I would like to convey our deepest condolences to his wife Graça Machel, the Mandela family and their friends, to the ANC and indeed to the entire South African nation," said De Klerk.

De Klerk and Mandela first met on December 13 1989, shortly before De Klerk became president, he said.

"We did not discuss any substantive issues and spent most of the time sizing one another up. We both reached the conclusion that we would be able to do business with one another."

At their next meeting in February of 1990, the two discussed Mandela's imminent release from prison. Mandela was released two days later, on February 11.

"He was initially taken aback and insisted that the release would have to be delayed to give the ANC time to make the necessary arrangements. I said that would not be possible but, in a spirit of compromise, agreed that he would be able to choose the place of his release.  He chose Cape Town.

"In the years that followed, it was an honour for me to have been able to work with Mr Mandela in the process that led to the adoption of the interim constitution and our first democratic elections in April 1994. Although we were political opponents – and although our relationship was often stormy – we were always able to come together at critical moments to resolve the many crises that arose during the negotiation process," said De Klerk.

'Great moral authority'
One such moment, he said, was the assassination of Chris Hani on April 10 1993, when Nelson Mandela "was able to use his great moral authority to call for calm and to ensure that the negotiations were not derailed".

In his concession speech, after the ANC's victory in our first nonracial election on April 27 1994, De Klerk congratulated Mandela on the role that he had played during the negotiations:

"Mandela will soon assume the highest office in the land with all the awesome responsibility which it bears. He will have to exercise this great responsibility in a balanced manner which will assure South Africans from all our communities that he has all their interests at heart. I am confident that this will be his intention," De Klerk said at the time.

"Mandela has walked a long road, and now stands at the top of the hill. A traveller would sit and admire the view. But the man of destiny knows that beyond this hill lies another and another. The journey is never complete. As he contemplates the next hill, I hold out my hand to Mr Mandela – in friendship and in co-operation.

"During his presidency, Mr Mandela did indeed use his great responsibility to assure South Africans from all our communities that he had all their interests at heart. He made a unique contribution not only to the establishment of our constitutional democracy but also to the cause of national reconciliation and nation-building.

"Nelson Mandela's courage, charm and commitment to reconciliation and to the Constitution, were an inspiration not only for South Africans but for the whole world. I believe that his example will live on and that it will continue to inspire all South Africans to achieve his vision of non-racialism, justice, human dignity and equality for all.

"Tata, we shall miss you – but know that your spirit and example will always be there to guide us to the vision of a better and more just South Africa."