Zindzi Mandela, the daughter of South Africa's anti-apartheid activists Nelson Mandela and Winnie Madikizela-Mandela, has died aged 59.

Per BBC News, the news was broken by public broadcaster SABC.

The news outlet reported in a statement: "The 59-year-old daughter of former president Nelson Mandela and struggle stalwart Winnie Madikizela-Mandela, passed away at a Johannesburg hospital in the early hours of this morning."

Her cause of death has not yet been revealed.

She was Nelson Mandela's sixth child and his second with wife Winnie Madikizela-Mandela.

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Zindzi was a South African politician who was serving as her country's ambassador to Denmark during the time of her passing on Monday (July 13).

Per the Daily Mail, Pule Mabe, a spokesperson for the African National Congress (ANC) said of Zindzi's passing: "This is untimely. She still had a role to play in the transformation of our own society and a bigger role to play even in the African National Congress."

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In a statement, South Africa's foreign affairs minister Naledi Pandor called Zindzi a "heroine". He said:

"Zindzi will not only be remembered as a daughter of our struggle heroes, Tata Nelson and Mama Winnie Mandela, but as a struggle heroine in her own right. She served South Africa well."

Zindzi was born in 1960 - just a year-and-a-half prior to father Nelson Mandella being incarcerated for the first time as a result of anti-government activities.

She first gained international prominence when she read out Nelson Mandela's rejection of then-president P.W. Botha's offer for freedom in 1985.

Her father had been offered a release from prison by Botha on the condition that he "unconditionally rejected violence as a political weapon".

At a public meeting, Zindzi read her father's response, saying: "What freedom am I being offered while the organization of the people [ANC] remains banned? Only free men can negotiate. A prisoner cannot enter into contracts."

Zindzi is survived by her husband, Molapo Motlhajwa, and her four children - Zoleka Mandela, Zondwa Mandela, Bambatha Mandela, and Zwelabo Mandela-Hlongwane - and her four grandchildren.

Our thoughts are with Zindzi's family, friends, and supporters at this difficult time...

Nelson Mandela's daughter Zindzi dies aged 59