How did King Ananda Mahidol of Thailand die?

Could someone please explain to me the death of King Ananda Mahidol of Thailand?

He was the elder brother of current King Bhumibol and he died at the age of 20 from what I have read… However, nothing I have read explains how… Articles just mention hints that it was an “unfortunate demise” and such…

According to Brittanica, he was found dead in bed on the morning of June 9, 1946 with a gunshot wound. The case was never fully explained.

This gives a little more information, but not much.

In part, it says:

How he died is documented. Who killed him is one of those things that will likely forever remain a mystery. Thais are said to believe that there is some sort of force (God, or something like that) that makes sure that the right person is always on the Thai throne. That’s probably why a lot of them don’t seem concerned about the current order of succession. Many want the elder Princess to become Queen once her father dies. But the succession will go to the Prince who is not seen by all as being regal material. There has been talk for some time of amending the Thai constitution to allow a female to take the throne. King Bhumibol Adulyadej (Rama X) has been on the throne for over 50 years now but his mother lived a very long time so it may be a while before we find out.