Carl von Hirschberg, who has died in Cape Town at the age of 91, wrote the Rubicon speech president PW Botha was supposed to deliver at the Natal congress of the National Party on August 15 1985.
A career diplomat, Von Hirschberg was deputy director-general in the department of foreign affairs at the time.
It was one of the most eagerly awaited speeches in the history of South Africa.
It would have signalled the government's commitment to end apartheid, release Nelson Mandela, unban the ANC and begin talks for democracy.
World leaders had been briefed by foreign affairs minister Pik Botha and Von Hirschberg himself, and the expectations of the world's media were sky-high.
Some 200 million people in South Africa and abroad settled in front of their TV screens and radios.
But instead of delivering the speech Von Hirschberg had written, PW unleashed a belligerent, finger-wagging rant vowing that South Africa's white population would fight for its survival and warning the world: "Don't push us too far."
The only part of Von Hirschberg's speech he used was a sentence at the end saying that "today we have crossed the Rubicon", which in the circumstances couldn't have been more tragically absurd.
Instead of being the most progressive and hopeful policy statement in the country's history, it was the most destructive. Violence surged, the rand collapsed, capital fled, sanctions were escalated and international banks called in their loans.
Von Hirschberg wrote the speech after being briefed on August 2 by an exuberant Pik on far-reaching policy changes agreed to at a meeting of ministers, senior party officials and PW, which the president was going to announce at the NP congress on August 15.
Von Hirschberg drafted a speech incorporating the momentous changes in language calculated to appeal to an international audience rather than the local party faithful.
Pik added the line about crossing the Rubicon, and sent it to PW.
Then he went off to Europe and the US to tell politicians that PW was going to be announcing "dramatic changes". Von Hirschberg, under the impression that the contents of his draft had been approved by PW, was sent to brief political leaders in Taiwan, Japan and Australia.
He got back in time to hear the broadcast and was "appalled". It was "nothing like" what he had written, he said.
Angry responses started coming in from UK prime minister Margaret Thatcher, US president Ronald Reagan, French president Francois Mitterrand, West German chancellor Helmut Kohl and other leaders, expressing their dismay and highlighting the pressure they were now under to intensify sanctions.
Von Hirschberg was told to draft replies. He went through the transcript of PW's speech looking for phrases "that could be interpreted, if you had an imagination, as containing something positive".
These he rewrote and incorporated into his responses.
The leaders were far from convinced and he had to draft replies to their replies, a process that went on for months.
Each of his replies was vetted by Pik and signed by PW.
"Every time we were called on to reply we [Von Hirschberg and Pik] extended the parameters of government policy little by little. It was a fascinating exercise."
Eventually the distilled content of his letters to the heads of state became a one-page synopsis of government policy according to which apartheid would be abolished and there would be negotiations for a new political system and democratic constitution.
When Von Hirschberg tried to report to ministers on the content of his letters he received a call from PW's office ordering him not to because the ministers didn't know anything about the policy changes reflected in the letters.
"My reply was unprintable," remembered Von Hirschberg. "We could tell heads of government what government policy was, but we dare not tell other ministers in the South African cabinet!"
Under growing Commonwealth pressure for sanctions, Thatcher sent the Eminent Persons Group to South Africa in 1986, with the very begrudging acquiescence of PW, to broker dialogue between the government and the ANC.
Von Hirschberg spent a lot of time with the group behind the scenes and finally there was agreement that the ANC and other liberation organisations would be unbanned and Mandela released.
But the night before the final meeting between the government and the EPG was due to be held, the South African Air Force bombed ANC targets in Lusaka, Harare and Gaborone.
Von Hirschberg was shocked and furious. He had no doubt that the raids were "a deliberate, pre-planned act designed to shipwreck the EPG initiative", which was immediately terminated. He felt that a "huge opportunity" to end violence and defuse pressure for sanctions was "thrown out of the window by the president and a few cohorts".
In 1987 he went to New York to sell to African ambassadors the progressive government policy contained in his synopsis. He felt he was making good progress but when he proposed a meeting of African foreign ministers it was vetoed by the department.
He decided he was wasting his time and retired from the foreign service.
He was asked to come out of retirement in 1990 to play a leading role in Namibia's transition to independence, and oversaw South Africa's hand-over of Walvis Bay to Namibia.
Von Hirschberg was born in Jamestown in the Eastern Cape on January 13 1926. He matriculated at Queens College in Queenstown and graduated from the University of Cape Town with a law degree in 1946.
He joined the department of foreign affairs in 1947 when he was 21.
He was posted to Vienna as South Africa's representative at the International Atomic Energy Agency, to New York as ambassador to the UN and to Tokyo as ambassador to Japan.
He is survived by three children. His first and second wives, Mary and Avril, died last year. 
1926 - 2017..