On 31 May 1961, the country became a republic following a referendum (only open to white voters) which narrowly passed; the British-dominated Natal province largely voted against the proposal. Queen Elizabeth II lost the title Queen of South Africa, and the last Governor-General, Charles Robberts Swart, became State President. As a concession to the Westminster system, the appointment of the president remained an appointment by parliament, and virtually powerless until P. W. Botha's Constitution Act of 1983, which eliminated the office of Prime Minister and instated a near-unique "strong presidency" responsible to parliament. Pressured by other Commonwealth of Nations countries, South Africa withdrew from the organisation in 1961 and rejoined it only in 1994.