A son of Angola's ex-President Jose Eduardo dos Santos has been arrested on suspicion of money-laundering, embezzlement of public funds and fraud.
Jose Filomeno dos Santos is the most high-profile person to be targeted in new President Joao Lourenco's campaign against alleged corruption.
He had been detained because of the "seriousness" of the allegations against him, Angolan prosecutors said.
He or his lawyers have not yet commented.
His Swiss-Angolan friend and business partner, Jean-Claude Bastos, was also arrested.
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In a statement, the state prosecutor said it is in a "preparatory investigation phase" in relation to the management of Angola's $5bn (£3.8bn) sovereign wealth fund by the ex-president's son and Mr Bastos.
"The evidence gathered resulted in sufficient indications that the defendants have been involved in practices of [alleged] various crimes, including criminal associations, receipt of undue advantage, corruption, participation in unlawful business, money laundering, embezzlement, fraud among others," the state prosecutor added.
Jose Filomeno dos Santos was sacked as head of the sovereign wealth fund in January, months after a BBC investigation into the fund and following an internal governance review.
Paradise papers link
He was also charged with fraud in March over the alleged transfer of $500m from the central bank to a UK bank.
He was not arrested at the time.
Last year, a BBC World Service and File on 4 joint investigations into the leaked Paradise Papers revealed that Mr Bastos received $41m in just 20 months for managing oil-rich Angola's sovereign wealth fund.
Mr Bastos, sometimes known as Jean-Claude Bastos de Morais, also used his position to help set up large investment deals he would stand to further profit from, the Paradise Papers documents showed.
Jose Filomeno dos Santos was the fund's chairman and chose Mr Bastos as its asset manager.
All sides denied any wrongdoing.
Jose Filomeno dos Santos was the second of the former president's children to be dismissed since Mr Lourenco took office.
His sister Isabel was removed as head of the state oil company Sonangol last year.
A billionaire, Ms Dos Santos is Africa's richest woman. It is not known how much her brother is worth.
Many of the former president's children have had government-linked roles.
Their father stepped down after 38 years in power last year. Mr Lourenco, also known as JLo, succeeded him with a promise of cracking down on corruption.
He has also developed a reputation for pushing aside powerful figures associated with his predecessor.
Angola is Africa's second-biggest oil producer.