14 August 1989
South African President, Pieter Willem Botha, resigned from his position as state president seven months after a minor stroke that led to his admission in hospital, and amid rising political instability, growing economic problems and diplomatic isolation. On 15 August, Mr. F.W. de Klerk was sworn in as Acting President pending the results of the general elections. In 1990 Botha resigned from the National Party (NP) in protest against President F.W. de Klerk's reform proposals which included the unbanning of some influential organizations such as the African National Congress (ANC), Pan Africanist Congress (PAC) and South African Communist Party (SACP) and the release of political prisoners, including Nelson Mandela.
References

O’Malley, P. ‘1989’, from Nelson Mandela Centre of Memory, [online], Available at www.nelsonamandela.org.za [Accessed: 05 August 2013]|SAHO, ‘P.W. Botha resigns from the National Party’, from South African History Online, [online], Available at www.sahistory.org.za [Accessed: 05 August 2013]|Nzo Alfred(1989), 'Resignation of PW Botha', from African National Congress, 15 August, [online],Available at www.anc.org.za [Accessed: 26 August 2013]