General elections for a constitutional assembly were held in April 1947, which the AFPFL won amidst a election boycott by the opposition, taking 173 of the 210 seats and running unopposed in over fifty constituencies. Aung San headed the constitutional assembly and was set to become Burma's Prime Minister, but was assassinated together with six other members of his cabinet on 19 July, a date commemorated as Martyrs' Day. U Nu succeeded Aung San as leader of the AFPFL and Premier of Burma.