But the Burmese armies, despite taking immense losses, could not break through for months. When Setthathirath and his army approached to relieve the city, Bayinnaung left Binnya Dala in command of the siege, and left with half his force to meet the enemy. On 8 May 1569, he decisively defeated Setthathirath northeast of the city, after which Lan Xang ceased to be of concern to the siege operations. Meanwhile, Maha Chakkraphat had died, and his son Mahinthrathirat made an offer of conditional surrender. It was refused. Bayinnaung demanded an unconditional surrender. Instead he sent one of his Siamese nobles to the city, pretending to be a deserter. King Mahinthrathirat promptly appointed him to a high command. Through the spy's treacherous machinations, one of the city's gates was opened. The city fell on that very night on 2 August 1569. Bayinnaung appointed Maha Thammarachathirat king of Siam on 29 September 1569.