The relationship started badly enough when Mandla Mandela, 38, was accused of bigamy when he wed French teenager Anais Grimaud while still married to his first wife.
Now the Frenchwoman has left him after the South African political chief discovered that the couple’s baby son was born to one of his own brothers.
The cuckold scandal is just the latest in a series of controversies involving Mandla Mandela, whom Nelson Mandela anointed as his political heir.
As well as being a South African MP, Mandla Mandela is a chief in the important Thembu tribe and handles much of Nelson Mandela’s legacy.
More significant, however, is that as grandson of the universally respected 94-year-old he is the public face of the Mandela family.
The 38-year-old politics graduate married his first wife, Tanda Mabunu-Mandela, at a traditional ceremony in 2004.
Six years later he married Mme Grimaud, who is from the island of Reunion, a French overseas territory in the Indian Ocean.
On marriage Madame Grimaud gained the tribal name Nkosikazi Nobubele Mandela.
The couple’s son was born in September last year and was named Qheya by Nelson Mandela himself.
The marriage was marred however, by the fact that at the time they tied the knot Mandla remained officially married to his first wife.
Ms Mabunu-Mandela fought the Grimaud marriage in the law courts and it was last year declared unlawful.
Mandla’s personal affairs became even more complicated last Christmas when he reportedly married a Swazi princess, Nodiyala Mbali Makhathini.
Until now both she and Madame Grimaud appeared to have been happy with this polygamous arrangement, although its precise legal status is unclear.
‘The Mandela family has sent my wife Nkosikazi Nobubele Mandela (nee Anais Grimaud) back to her home after it was discovered she has been having an affair with one of my brothers’, the statement read.
‘I confirm this affair resulted in a son that Nkosikazi Nobubele gave birth to in 2011. I can also confirm DNA tests conducted have confirmed the child is not mine.
‘The revelation of this affair has come as a shock to me and the rest of my family. It has been made more painful because it is my own brother who is at the centre of the crisis.’
The statement did not identify which of Mandla Mandela’s three brothers is the father.
Mandla is the oldest, born in 1974, followed by Ndaba (1983), Mbusu (1991) and Andile (1993).
Ndaba Mandela was quoted in The Sowetan as saying the child was not his, adding: ‘Nobody knows who the father is, but I can confidently confirm that it was not me.
‘Mandla told me that he was not the father. She [Grimaud] left because of their problems, the child’s paternity was probably one of the main reasons. I have never touched her in a physical or sexual way.’
Mandla is the first son of Makgatho Lewanika Mandela, an attorney who died of Aids in 2005. His second wife, Hi Zondi Mandela, died in 2003 and, at first, her cause of death was given as pneumonia.
After Makgatho’s death, Mandla announced that her pneumonia had been a complication of ther HIV virus.