title: 1960 South African republic referendum
context: A referendum on becoming a republic was held in South Africa on 5 October 1960. The Afrikaner-dominated right-wing National Party, which had come to power in 1948, was avowedly republican, and regarded the position of Queen Elizabeth II as head of state as a relic of British imperialism.[1] The National Party government subsequently organised the referendum on whether the then Union of South Africa should become a republic. The vote, which was restricted to whites, was narrowly approved by 52.29% of the voters.[2][3] The Republic of South Africa was constituted on 31 May 1961.
question: When did South Africa become a republic?
answers: 31 May 1961