Flag of the Transvaal and the South African Republic; the "Vierkleur"
Source: Drawn by SKopp / 

Reference: https://www.fotw.info/flags/za-trans.html, http://savaflags.org.za/spec/Zuid%20Afrikaansche%20Republiek%20-%20national%20-%201858%20-%201902%20-%20sheet%201.pdf
Himasaram