Zindzi Mandela, the daughter of South Africa’s first black president and revolutionary anti-apartheid leader Nelson Mandela, has died at the age of 59.

She died at a Johannesburg hospital on Monday morning but the cause of death has not been made known, state television South African Broadcasting Corporation has reported. 

Zindzi came to international prominence in 1985, when the country’s white minority government offered to release her father from prison if he denounced violence perpetrated by the African National Congress against apartheid in South Africa.

At the time, she read out her father’s letter of rejection that was broadcast around the world. 

She studied law at the University of Cape Town and also worked as an anti-apartheid activist.

For a short period, she also served as South Africa’s First Lady following her father’s presidential election in 1994 and her parents’ divorce until 1998. 

Zindzi, who was Mandela’s sixth child and his second with fellow anti-apartheid leader and politician Winnie Madikizela-Mandela, had been serving as South Africa's ambassador to Denmark. 

She leaves behind her husband Molapo and four children Zoleka, Zondwa, Bambatha and Zwelabo.  

Bambatha paid tribute to his mother on Instagram, writing, ‘Lala ngo xolo Madlomo,’ which translates to, ‘Sleep in peace Madam’.

South Africa's foreign affairs minister Naledi Pando 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.”