JOHANNESBURG — Nelson Mandela's 13-year-old great granddaughter was killed in a car crash early Friday after South Africa's World Cup concert, his office said. "Zenani Mandela, 13, was travelling in a car returning from the World Cup kick-off concert at Orlando Stadium when the accident occurred. There was only one car involved and no one else was injured," The Mandela Foundation said in a statement. She was the granddaughter of Zindzi Mandela, daughter of South Africa's first black president. "Zenani, who celebrated her 13th birthday on June 9, was the eldest child of Zoleka Seakamela and one of Mr Nelson Mandela?s nine great grand-children," it said. "The family has asked for privacy as they mourn this tragedy."