He has lived there since 1989 and has a US citizenship since 2002.
One can always obviously argue that it doesn't count and that he is South African because of his Father and because he was born there, and/or Canadian because his mother is Canadian, but in that case the telephone is a Scottish (Alexander Graham Bell), gramophone a Russian (Emile Berliner) and the zipper a Swedish (Gideon Sundback) invention - all made by US immigrants with citizenships.