Malta became independent on 21 September 1964 (Independence Day). Under its 1964 constitution, Malta initially retained Elizabeth II as queen, with a governor-general exercising authority on her behalf. On 13 December 1974 (Republic Day) it became a republic within the Commonwealth, with the President as head of state. On 31 March 1979, Malta saw the withdrawal of the last British troops and the Royal Navy from Malta. This day is known as Freedom Day and Malta declared itself as a neutral and non-aligned state. Malta joined the European Union on 1 May 2004 and joined the Eurozone on 1 January 2008.