Establishment of the Anglo-American Committee of Inquiry was announced in Washington and London on 13 Nov 1945, after considerable diplomatic negotiation. The membership of the Committee was made public on 10 Dec 1945.
For a detailed review of those negotiations see, Cohen, “The Genesis of the Anglo-American Committee on Palestine, November 1945: A Case Study in the Assertion of American Hegemony”, The Historical Journal, Vol. 22, No. 1 (Mar., 1979), pp. 185-207.