From being portrayed in the past as a kindly uncle acting as the mentor to his nephew President Kim Jong-un, the self-styled army general was rapidly toppled from power and branded an "eternal traitor", declared a non-person and brutally executed by firing squad.
Although purges of that kind are commonplace in the secretive Communist dictatorship, Jang's fall from grace took place in public and was accompanied by a 2700-word charge sheet that did not just portray him as a traitor but execrated him as a decadent and depraved hedonist with capitalist leanings. It all happened in the presence of news cameras - from the moment he was arrested by two grim-looking policemen in the national assembly in the capital Pyongyang to his appearance two days later handcuffed in court. Judging by his dark puffy eyes - the obvious result of a beating - his fate was all too obvious. No doubt footage exists of his execution but so far that has not been released, the most likely method of execution being by machine-gun firing squad.
This speaks volumes about the way the young president wanted this particular episode to be portrayed. Normally political enemies are simply eliminated together with their families and once the deed has been done the news is released as a warning to others. Jang's fate was different but it is no less chilling for that. Not only was he a well-known face among the apparatchiks who regularly stood unsmilingly behind the president, but he was also one of the in-crowd, being married to Kim Kyong-hui. sister of the previous President Kim Jong-Il and aunt of the present president.
That closeness to the seat of power should have protected Jang, and to a certain extent it did. In 2004, he survived a period of political purging and emerged two years later as a powerful member of the North Korean Workers Party, one of the leading institutions that determine North Korean policy. By 2009, he had been elected vice-president of the all-powerful National Defence Commission (NDC), a position that afforded him considerable political power when Kim Jong-un became president two years ago.
Not only was he regarded as the real power behind the new and untested leader, but his age and experience gave him considerable authority within the corridors of power in Pyongyang. Another political prop was his understanding of the need to maintain strong bilateral links with China, the only country that is prepared to act as North Korea's main ally. That could have been his undoing, as Kim Jong-un is distrustful of the links with Beijing, and feared valuable North Korean mineral resources were being bartered at too low a value.
Nevertheless, despite those suspicions, Jang seemed to be in an almost unassailable position. Yet last Thursday North Korean state media announced he had been executed. For good measure, the official communique blackened his name by alleging that the "despicable human scum Jang, who was worse than a dog, perpetrated thrice-cursed acts of treachery in betrayal of such profound trust and warmest paternal love shown by the party and the leader for him". He was accused of having committed "anti-party, counter-revolutionary factional acts", harbouring "politically-motivated ambition", weakening "the party's guidance over judicial, prosecution and people's security bodies", and obstructing "the nation's economic affairs", including "illicit affairs with women."
These are strong words suggesting a rapid and disastrous fall from grace, but behind the customary character assassination - which included him being immediately air-brushed from official photographs - there is more to Jang's demise than a blip in North Korean domestic politics. Any turbulence in Pyongyang is bound to cause tremors elsewhere, largely because Jang was not just another disgraced politician in a rogue state who had fallen foul of authority or had lost his backing. He was related to the president, albeit by marriage, and he occupied a position of huge authority, being the de facto second-in-command and a politician who was bound to have created and maintained a series of powerful alliances within the country's political hierarchy.
More than anything else, that is the main reason why Kim had to act with extreme prejudice against his uncle. The arrest could not be done as if Jang were a thief in the night; it had to be carried out publicly and brutally, both to show the people of North Korea that the president meant business and as a warning to any of Jang's remaining allies.
It has to be remembered, too, that Jang was not always a kindly avuncular party hack who had the best interests of his nephew at heart. Jang and his widow Kim Kyong-hui were hardline revisionists who were schooled in the Stalinist tradition and were never interested in making concessions to the rest of the world - apart, that is, from currying favour in China. They were also ruthless in hanging on to power and were completely uninterested in the welfare of the people - during the famines that swept through the country 20 years ago they supported the use of force to quell public disturbances even though up to three million North Koreans were dying of starvation. Their only commitment to improving the country's economy lay in exchanging mining concessions for food supplies when South Korea attempted rapprochement during its "sunshine" policies at the beginning of the century.
That also helps to explain the ruthlessness and rapidity of Jang's fall from grace. During his own rise to power he made enemies of many fellow hardliners in government, notably the elderly chief of the general staff, Marshal Ri Yong-ho, who disappeared a year ago. The official reason for this is that he was suffering from a terminal illness, although Chinese sources claim he is under house arrest for "counter-revolutionary crimes".
Having made so many enemies, it is entirely possible that Jang's arrest and execution were part of a hardline coup aimed at strengthening the position of the armed forces and in so doing bolstering Kim's presidential power. If that is the case, and nothing in North Korea is ever straightforward, it could signal further purges and the onset of a new power struggle. It is almost certain that in the weeks to come other politicians and officials close to Jang will face arrest, imprisonment or worse. As it is customary to punish both the alleged culprit and their families, the shock waves will be felt across the North Korean political community.
In the longer term that will mean more misery and depredation for the ordinary North Koreans, as there is bound to be a strengthening of the "military first" programme. This ruinous policy allows at least one-third of the country's GDP to be spent on the armed forces and the development of nuclear weapons, all at the cost of improving the country's infrastructure.
That can hardly be the best outcome for North Korea's neighbours - especially South Korea, which is always the country most likely to be affected by any change in the balance of regional geo-strategic power. Officially the two countries are still in a state of conflict, and like his father before him Kim has made no secret of his desire to rule over a united country as the "Supreme Leader". Whenever he feels insecure it is usually the signal for a display of bellicosity aimed at producing a flashpoint that can then be exploited. So far, the mood in the South Korean capital Seoul is one of resignation mixed by a fear that Jang's removal will introduce a period of instability. At worst this could include provoking aggression between the two countries with cross-border attacks or other military demonstrations.
Only one thing is certain. North Korea remains one of the most secretive and closed societies in the world. Tight controls are in place to prevent information getting out of the country, defectors are few and far between and there are heavy punishments for those who are found to be attempting to evade the rules. The state monopolises the transmission of all information relating to the government and very little information of any importance gets out of the country. It is even possible that the ousting of Jang happened some time ago and the news was carefully orchestrated by intelligence services.
For observers like Jasper Kim, the founder of the Asia-Pacific Global Research Group, North Korea this weekend is "a Rubik's Cube that no-one can solve". He says it is impossible to be sure what will happen next. His own view is deeply pessimistic: "What history tells us is that when it does happen, it will be unexpected and extreme, and everyone must be prepared for the worst-case scenario."