Kim was responsible for the death of his aunt Kim Kyong Hui, one of the most senior officials to defect has said.

His aunt was married to Jang Song Thaek, who was executed in 2013 as the new Supreme Leader carried out a purge of officials and family.

Kim had Jang, his one-time political mentor and described as the second most powerful figure in North Korea, killed on an array of charges including treason and corruption.

But the un-named defector claimed on America’s CNN: “ On May 5th or 6th of last year, Kim Jong-un ordered his aunt, Kim Kyong Hui, to be killed.

“Only his bodyguard unit, Unit 974, knew this. Now senior officials also know she was poisoned.”

It had been reported last November that Ms Kim, 68, died from a stroke during an impassioned argument about her husband’s execution.

She was a close aide to her brother Kim Jong-il for decades, assuming senior positions in the party and becoming a four-star general in 2010.

The stroke claims were made by earlier defector Kang Myung-do, son-in-law to North Korea’s ex-Prime Minister, Kang Sun San.

Korean media reported she committed suicide five days after her husband’s execution.

But it’s now been claimed Ms Kim was murdered after she complained about her 67-year-old husband’s death.

The latest defector to speak out also said Kim Jong-un’s uncle was arrested, tried and executed in an “underground secret room” in less than a week.

After his execution, direct family members were said to have been shot dead and other relatives were sentenced to labour camps.

Ms Kim was frequently seen at the side of her nephew and his wife at public events until January last year, when her last public appearance was in the documentary shown on North Korean Central TV.

She was seen walking with the leader and his wife towards the Kumsusan Palace of the Sun in the capital, Pyongyang, to pay tribute to the embalmed bodies of former leaders Kim Il-sung and Kim Jong-il.

The Kim family has ruled the reclusive, impoverished state for more than six decades with an iron fist and a pervasive personality cult.

Mrs Kim, often the only female face on official photographs of ranks of generals and party leaders, was tasked with transforming her nephew into a figurehead with a reputation for strong military tactics who is able to handle an international crisis.

She also owned the only burger restaurant in Pyongyang, where the menu offers “minced meat and bread” rather than using the American word ‘burger’.

She met her husband at university and married in 1972.           

They have no surviving children, according to the South Korean government-run Information Centre on North Korea.

Their only child, a daughter, committed suicide in 2006 at the age of 29 while studying in Paris, according to South Korean media.