Seeing you are born in South Africa, this might be the marriage record of your great grandfather:
"South Africa, Dutch Reformed Church Registers (Cape Town Archives), 1660-1970 ," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:XK45-N31 : 6 August 2017), Jacobus Stephanus Bosman Roos and Lilian Alice Van Zyl, 16 Aug 1932, Marriage; citing p. , Cape Town, Cape of Good Hope, South Africa, State Archives, Cape Province; FHL microfilm 2,214,040.
And, as Ros and Marion said, more names, dates, and places would be extremely helpful!