 His paternal great-grandfather, Jan van Rooy, had been a senator, while his paternal grandfather, Willem, had been a clergyman who fought in the Anglo-Boer War and who stood twice, unsuccessfully, as a National Party candidate.His paternal aunt's husband was J. G. Strijdom, a former Prime Minister.His own father, Jan de Klerk, was also a Senator, having served as the secretary of the National Party in Transvaal, president of the senate for seven years, and a member of the country's cabinet for fifteen years under three Prime Ministers.