Dawson, who supported the "gentle growth of euthanasia", admitted in the diary that he ended the King's [George V] life:

At about 11 o'clock it was evident that the last stage might endure for many hours, unknown to the Patient but little comporting with that dignity and serenity which he so richly merited and which demanded a brief final scene. Hours of waiting just for the mechanical end when all that is really life has departed only exhausts the onlookers & keeps them so strained that they cannot avail themselves of the solace of thought, communion or prayer. I therefore decided to determine the end and injected (myself) morphia gr.3/4 and shortly afterwards cocaine gr.1 into the distended jugular vein ... In about 1/4 an hour – breathing quieter – appearance more placid – physical struggle gone.

Dawson wrote that he acted to preserve the King's dignity, to prevent further strain on the family, and so that the King's death at 11:55 PM could be announced in the morning edition of The Times newspaper rather than "less appropriate ... evening journals". Neither Queen Mary, who was intensely religious and might not have sanctioned euthanasia, nor the Prince of Wales was consulted. The royal family did not want the King to endure pain and suffering and did not want his life prolonged artificially but neither did they approve Dawson's actions. British Pathé announced the King's death the following day, in which he was described as "for each one of us, more than a King, a father of a great family".

(from Wikipedia)