Sultan Hisamuddin resumed his reign in September 1945. In the same year, he signed the Malayan Union treaty, albeit under protest, along with the rest of the rulers of Malaya at the time.[21] He later rejected the establishment of Malayan Union and openly supported the Malay nationalists who opposed the plan.[2] In 1950, he demolished Mahkota Puri Palace and built Istana Alam Shah, which is still used as the official residence of the Sultan of Selangor to this day.[3]