Story highlights Kim Kyung Hee was the sister of Kim Jong Il

Kim Jong Il died three years ago and left his son in power

His son executed Kim Kyung Hee's husband, who is his uncle

The aunt of North Korean leader Kim Jong Un suffered a fatal stroke while she was on the phone with him, arguing about her husband's execution, according to a defector from the secretive nation.

Kim Kyung Hee was the sister of Kim Jong Il, the North Korean leader who died three years ago and left his son in power.

Her husband, Jang Song Thaek, was executed in December, shocking many observers around the world.

Jang, the younger leader's uncle by marriage, was considered instrumental in his rise to power.

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Before his execution, he was described as the second-most powerful figure in North Korea.

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But the young leader turned his back on Jang in spectacular fashion late last year, having him executed on charges that he tried to overthrow the government.

"In the seething period of the effort for building a thriving country last year, we took the resolute measure of removing the factionalists," the North Korean leader said in a New Year's address shortly after the execution.

Days after the execution, Jang's wife suffered her third stroke, according to Kang Myung-do, a defector who was son-in-law to North Korea's ex-Prime Minister, Kang Sun San.

She was on the phone with the North Korean leader when she suffered the stroke, Kang said. She was hospitalized and later died.

CNN could not independently confirm the defector's information.

The death was not announced because she died a few days after her husband and the government did not want people to link her death to his, according to the defector.

Korean media have reported that she committed suicide five days after her husband's execution.