The Democratic Alliance replaced its defected Cape Town metro chairman Grant Pascoe on Tuesday with Shaun August, a councillor from Steenberg.
Pascoe was on Monday reported to have left the DA to join the ruling party.
"Councillor August has been actively involved in politics for more than a decade, he has been instrumental in various election campaigns across the country," said DA spokeswoman Mart-Marie Haasbroek.
August had also served as the deputy chairman on the DA metro executive council since 2012.
"He will remain the acting chairperson for the DA metro council until the annual general meeting later this year. A new metro council will then be elected," Haasbroek said in a statement.
Responding to his appointment, August said he was committed to working with all the residents of the city.
"As the councillor for Ward 67, which includes nine informal settlements, I have a unique understanding of the needs and challenges of the residents," August said.
He said he knew the DA was a strong party.
"We are united as one big blue machine to take us further and maintain and increase the DA support in the metro and the Western Cape," said August.
Cape Town Mayor Patricia de Lille said on Monday she was not informed by Pascoe of his intentions to jump ship.
She claimed that Pascoe had "chosen to find a new political home due to his inability to live up to the standards required of DA public representatives."
She listed what she described as several shortcomings in his performance.
The African National Congress, which announced Pascoe's defection, welcomed him into the party.
"Councillor Pascoe joins an overwhelming number of South Africans, who despite finding themselves in other political parties, recognise the ANC as the only organisation with the track record, capacity and determination to build a South Africa," spokesman Jackson Mthembu said in a statement.
"Comrade Pascoe joins as an ordinary member of the organisation, and will assist our efforts to win back the Western Cape."
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