Kim Jong Un's uncle has been executed, with the state media calling the leader's former mentor "worse than a dog".
The announcement early today comes days after Pyongyang announced that Jang Song Thaek had been removed from all his posts because of allegations of corruption, drug use, gambling, womanising and generally leading a "dissolute and depraved life".
Mr Jang was considered the second most powerful official in the North.
He was seen as helping Kim Jong Un consolidate power after the death of his father, Kim Jong Il, two years ago.
Some analysts see the purge as a sign of Kim Jong Un'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 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 Jong Un's government against Washington, Seoul and Tokyo, including vows of missile and nuclear strikes and warnings that Pyongyang would restart nuclear bomb fuel production.
Mr Jang was married to Kim Jong Un's aunt, Kim Kyong Hui, the younger sister of Kim Jong Il.
He was earlier 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.