Duduzane Zuma, the son of former president Jacob Zuma, took to the witness stand in the Randburg Magistrate's Court on Wednesday to give his version of events on the day Phumzile Dube died in an accident.
Zuma is on trial for culpable homicide, after an accident which caused the death of Dube in February 2014. His car crashed into a taxi in which she was travelling.
Zuma told the court that he is not guilty of the charge.
During cross-examination by State prosecutor Yusuf Baba, Zuma told the court that on the day of the incident, there was heavy rain and visibility was poor. He said he was travelling from Fourways to Saxonwold and had joined the highway from William Nicol Drive.
He also told the court that he had been driving at a speed of about 120km/h and had hit a puddle of water, which resulted in his vehicle losing control and spinning.
He said his car spun and hit an "object". He did not recall what exactly the object was.
When Baba asked whether he was aware that he had hit a taxi, Zuma said he would not deny or admit whether he had hit it.
Zuma also told the court that it had been impossible for him to bring the car back under control following the crash.
He said, in his view, it had been impossible to avoid the crash.
Zuma described the incident as traumatic for everyone, saying he was fortunate to have not been killed or injured.
"It does have an effect on me," he added.
However, he said he did not want to play the "blame game" and took full responsibility.
"I do sympathise with anyone who has been affected," he told the court.
The matter was postponed to Thursday, due to technical challenges with the recording machine.