Southern Ireland
According to the British he met the Lord Lieutenant and was made the King's prime minister.   According to the Irish viewpoint, Collins went to accept the surrender of Dublin Castle. Arthur Griffith became President of Dáil Éireann, and then both Dáil Éireann and the House of Commons of Southern Ireland were then replaced in a  new election, for the 'Third Dáil', sometimes called the 'Provisional Parliament' or the 'Constituent Assembly'.  When Griffith died and a week later Collins was assassinated both in August 1922, W.T. Cosgrave was appointed to both offices, so the Irish nationalist and the British both systems of government joined into one temporary system, until the 1922 Constitution of the Irish Free State came into force in December 1922.