Bhumibol was born at Cambridge Hospital (now Mount Auburn Hospital) in Cambridge, Massachusetts, in the United States, on 5 December 1927.He was the youngest son of Prince Mahidol Adulyadej, the Prince of Songkla, and his commoner wife Mom Sangwan (later Princess Srinagarindra, the Princess Mother). His father was enrolled in the public health program at Harvard University, which is why Bhumibol was the only monarch to be born in the United States of America.Bhumibol had an older sister, Princess Galyani Vadhana, and an older brother, Prince Ananda Mahidol.