The powerful uncle of North Korean leader Kim Jong Un has been removed amid claims of corruption, drug use and a long list of other "anti-state" acts.
The purge apparently ends the career of Jang Song Thaek, the country's second most powerful official, and leaves Kim without the man long considered his mentor as he consolidated power after his father's death two years ago.
Jang Song Thaek's fall from grace, detailed in a lengthy dispatch by state media, is the latest and most significant in a series of reshuffles that Kim has conducted in an apparent effort to bolster his power.
Some analysts see the purge as a sign of Kim's growing confidence, but there has also been fear in Seoul that the removal of such an important part of the North's government - seen by outsiders as the leading supporter of Chinese-style economic reforms - could create dangerous instability or lead to a major miscalculation or attack on the South.
Tensions are still high on the Korean Peninsula following a torrent of threats in March and April by Kim's government against Washington, Seoul and Tokyo, including vows of missile and nuclear strikes and warnings that Pyongyang would restart nuclear bomb fuel production.
South Korean intelligence said days ago that a purge was likely because two of Mr Jang's aides had been executed last month for corruption. A recent state documentary in the North had all images of Mr Jang removed.
Mr Jang, who is married to Kim Jong Un's aunt, Kim Kyong Hui, the younger sister of the late Kim Jong Il, was described by state media as "abusing his power", being "engrossed in irregularities and corruption" and taking drugs and squandering money at casinos while undergoing medical treatment in a foreign country.
The dispatch also said he had "improper relations with several women and was wined and dined at back parlours of deluxe restaurants".
Referring to North Korea as a "popular democratic dictatorship", the dispatch said "Jang seriously obstructed the nation's economic affairs and the improvement of the standard of people's living". Kim has vowed to lift the country from poverty while also pursuing a nuclear weapons programme that has drawn worldwide criticism - and heavy economic sanctions.
The decision to strip Mr Jang of all posts and titles and expel him from the ruling Workers' Party was made at a Political Bureau meeting of the party's Central Committee. The dispatch also indicated that the purge would extend to supporters of Mr Jang, but did not provide details.
Opinion has been divided among analysts on what the purge may mean for the future of North Korea. Some analysts believe it shows a weakened Kim fending off challengers, but others say it indicates the young leader's growing strength.
"I believe it shows Kim Jong Un is firmly in control and confident enough to remove even the senior-most officials," said Bruce Klingner, an Asia specialist at the conservative Heritage Foundation think-tank in Washington.
But he added: "There is no reason to believe with this latest ouster that there will be a change in North Korean policy; that the Kim dynasty will suddenly turn around its bad behaviour."
Mr Jang has held a string of senior jobs, including membership in the National Defence Commission, the government's top ruling body. He served as a leading economic policy official in charge of the push to draw foreign investment, traveling in 2012 to China to discuss the establishment of special economic zones. Over the past, he assumed responsibility for North Korea's burgeoning sports industry, a pet project of Kim's.
He has also reportedly been purged several times previously, only to return to power. But the formality and length of the current allegations against him suggest a more serious development.
Kim has reportedly overseen other purges of senior officials, though none as high profile as this one.
One of the most notable personnel changes was the 2012 sacking of military chief Ri Yong Ho, who was once also dubbed a mentor to Kim. State media said he was dismissed in July 2012 due to an unspecified illness, but analysts speculated that he was purged because Kim wanted to reshape the power structure.
The North publicly executed 17 people last year and 40 this year, according to politicians briefed by South Korea's spy agency last week.