Bhumibol ascended the throne following the death by gunshot wound of his brother, King Ananda Mahidol, on 9 June 1946, under circumstances that remain unclear. While a first government statement declared that Ananda had accidentally shot himself,[21] an investigation committee ruled that this was impossible.[22] Two palace aides were convicted of regicide and executed. A third feasible explanation, that Bhumibol accidentally shot his brother while the boys played with their guns, was never seriously considered, as such an implication could have strongly damaged the institution of monarchy.[23]
Bhumibol succeeded his brother, but returned to Switzerland before the end of the 100-days mourning period. Despite his interest in science and technology, he changed the subject and enrolled in law and political science to prepare for his duties as head of state. His uncle, Rangsit, Prince of Chainat, was appointed Prince Regent. In Bhumibol's name, Prince Rangsit authorized a military coup that overthrew the government of Thamrongnawasawat in November 1947.[24] He also signed the 1949 constitution, which gave back to the monarchy many of its powers that had been taken away by the 1932 Revolution.[25]
While finishing his degree in Switzerland, Bhumibol visited Paris frequently. It was in Paris that he first met Mom Rajawongse Sirikit Kitiyakara, daughter of the Thai ambassador to France.[26]
On 4 October 1948, while Bhumibol was driving a Fiat Topolino on the Geneva-Lausanne road, he collided with the rear of a braking truck 10 km outside Lausanne. He hurt his back and incurred cuts on his face that cost him the sight of his right eye.[27][28] While he was hospitalised in Lausanne, Sirikit visited him frequently. She met his mother, who asked her to continue her studies nearby so that Bhumibol could get to know her better. Bhumibol selected for her a boarding school in Lausanne, Riante Rive. A quiet engagement in Lausanne followed on 19 July 1949, and the couple were married on 28 April 1950, just a week before his coronation.
Bhumibol and his wife Queen Sirikit have four children:
(Formerly HRH) Princess Ubolratana Rajakanya, born 5 April 1951 in Lausanne, Switzerland; married Peter Ladd Jensen, has 2 daughters. Her autistic son, Bhumi Jensen, was killed in the tsunami caused by the 2004 Indian Ocean earthquake.[29][30]
HRH Crown Prince Maha Vajiralongkorn, born 28 July 1952; married Mom Luang Soamsawali Kitiyakara (later divorced and became HRH the Princess Niece); 1 daughter. Then married Yuvadhida Polpraserth; 4 sons and a daughter. Third marriage was to Srirasm Akharapongpreecha; one son.
HRH Princess Maha Chakri Sirindhorn, born 2 April 1955; unmarried
HRH Princess Chulabhorn Walailak, born 4 July 1957; married Virayudh Tishyasarin, (then divorced); 2 daughters