Nelson Mandela's grandson, Mandla, and his wife, Rabia, announced the birth of their twins on Friday.
"We are overjoyed today to welcome our new bundles of joy," the Mandelas said in a statement.
"(Mandela Ikraam) Mandela is now a big brother, and Mvezo Komkhulu is about to hear the pitter-patter of little feet again. Our family is growing by 20 more fingers and 20 more toes.
"The Royal House of Mandela is truly grateful for these blessings, Alhamdulillah (Praise to Allah). Jummah Mubarak (Blessed Friday)!" the family said.
They indicated that they had had a boy and a girl.
The couple had their first child, whose full name is Mntwanenkosi Mandela Ikraam Mandela, in May 2017, News24 reported at the time.
Mandela married Rabia, his fourth wife, in 2016.