A North Korean expert discussed with Fox News Digital why Kim Jong Un’s sister, Kim Yo Jong, is "the most dangerous woman in the world" after surprise appearance in Russia last week.

"I argue that Kim Yo Jong today is indeed the most dangerous woman in the world in all of Korean history, perhaps world history," said Sung-Yoon Lee, a Fellow at The Woodrow Wilson International Center for Scholars.

"Although she is relatively young – she turns 36 at the end of September – she is a woman who brings, of course, a softer image to the brutish, chauvinistic, male-dominated facade of her nation," he said. "She is to be taken very seriously."

Lee is the author of "The Sister," which tracks Yo Jong’s rise to power as "de-facto deputy" to the hermit kingdom’s supreme leader.

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Kim Yo Jong made her first public appearance in 2011 with her father, Kim Jong Il, but remained a largely background figure until she appeared at the Winter Olympics in Pyeongchang, South Korea, in 2018. She then months later accompanied her brother to a historic summit with South Korean President Moon Jae-in.

She most recently accompanied her brother to Russia for his summit with Vladimir Putin, visiting the Vostochny Cosmodrome ahead of a meeting between the two leaders.

Analysts have identified Kim Yo Jong as a possible successor to her brother, and Lee believes she may serve as a regent to her brother’s rumored children until they are old enough to take power – even if that creates some tension.

North Korea sister

The cover of "The Sister" by Sung-Yoon Lee from Pan Macmillan publishers. (Pan Macmillan)

Lee acknowledged that if there is "some tension with the aunty" then she will "remember the bitter, cold winter of 2013 when she and her brother had their uncle executed."

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Kim Yo Jong and her brother have seemed to increasingly cooperate over the years, starting with the assassination of their uncle who had "half-heartedly clapped" while in the presence of the supreme leader – just one of the several crimes for which state media accused him of using an "arrogant" action that touched off "towering resentment of our service personnel and people."

North Korean leader Kim Jong Un signs the visitors book next to his sister, Kim Yo Jong, during their visit to the Vostochny Сosmodrome to meet with Russian President Vladimir Putin on Sept. 13, 2023. (Sputnik/Artem Geodakyan/Pool via Reuters)

Following her public debut abroad in South Korea, she has made bold declarations on behalf of her brother and his government – 40 written statements, at least, as well as ordering the destruction of a joint liaison office located in North Korean territory.

Lee explained that this vested authority is particularly troubling since it likely gives her authority – even jointly with her brother – over the country’s nuclear weapons arsenal, to which she referred in a couple of statements last year when threatening South Korea if it "fired even a single bullet inside North Korean territory."

Armed Forces Ceremony

North Korean leader Kim Jong Un and his sister, Kim Yo Jong, participate in an event to confer "Paektusan" commemorative pistols to leading commanding officers of the armed forces on the 67th anniversary of the signing of the Korean War armistice, July 27, 2020, in Pyongyang. (KCNA via Reuters)

"We have never seen this in North Korea, in Korean history, in world history, a female co-despotess – a female co-leader of a criminal regime – issuing nuclear threats and saying that I have the authority to nuke you, a peaceful, democratic neighboring state in South Korea," Lee said.

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Researching a subject from one of the most secretive nations on the planet proved difficult, but Lee worked through the "great difficulty" with the help of graduate students to research "every single reference to Kim Yo Jong" in Chinese reports and even on Taiwan, official statements from North Korea and "hundreds of hours" of North Korean video.

Kim Yo-Jong Politics

Kim Jong Un attends the completion of a fertilizer plant with his sister, Kim Yo Jong, in a region north of the capital, Pyongyang, on May 2, 2020. (KCNA via Reuters)

"From all these videos, footage and North Korean statements and so on, I see Kim Yo Jong as occupying a uniquely powerful position in her nation's hierarchy," Lee said. "I've also interviewed several people who have met her and was able to glean some insights into her personality and so on, but I will admit that there are limitations to my book and in general to studying North Korea."

His research yielded interesting finds, such as the tension that arises from a powerful female leader in a heavily "chauvinistic, male-dominated culture and society," which Lee argued would fall "second to maintaining rule within the royal family."

Hermit Kingdom summit

Kim Yo Jong shakes hands with South Korean presidential national security director Chung Eui-yong at the northern side of the border village of Panmunjom in the demilitarized zone, North Korea, on June 12, 2019. (KCNA via Reuters)

"North Korea itself, its existence is shocking because it's such a unique country – so unique, so different, so unconventional that I often refer to North Korea as uniquely unique," Lee said. "North Korea is really different."

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North Korea Russia

Kim Yo Jong arrives at the Vostochny Сosmodrome before a meeting between Russian President Vladimir Putin and Kim Jong Un on Sept. 13, 2023. (Sputnik/Vladimir Smirnov/Pool via Reuters)

Lee speculated that North Korea could weaponize Kim Yo Jong, sending her to meetings with the president or at the United Nations, which would put those governing bodies in the awkward position of accepting her or appearing "petulant" for the fact she’s a woman, further cementing her power and influence.

"When she says, 'OK, let's talk about denuclearization or normalization of diplomatic relations,' many of us will be prone to wanting to believe her just because she is a woman," he said. "So, she is ambitious, she is smart, she is ruthless and, therefore, we should take her very seriously and not patronize her."