As rumors swirl around the health of North Korean leader Kim Jong Un, his sister, Kim Yo Jong, could possibly take the helm of the isolated Asian country. Kim Yo Jong is in charge of propaganda affairs and has accompanied her brother on several high-profile trips.

Earlier in April, she was named an alternate member of the ruling Workers’ Party’s powerful Central Committee Politburo. She has also served an unofficial role as her brother’s chief of staff.

Kim Yo Jong, 31, made headlines in March, when she criticized South Korea for opposing a live-fire military demonstration by Pyongyang.

“As far as I know, the South side is also fond of joint military exercises and it is preoccupied with all the disgusting acts like purchasing ultra-modern military hardware,” she said in an official statement directed at Seoul. She also described South Korea’s government as “a mere child” and “a burnt child dreading fire.”

She has attended multiple summits between her brother and other world leaders such as President Donald Trump, South Korean President Moon Jae-in and Chinese President Xi Jinping. During a summit with Moon in 2018, she gave her brother a pen when he signed the guestbook, along with flowers he had been handed at the border of the two countries. The visit caused speculation that she could be the most influential individual in the North Korean government behind her brother.

At the same time, she may struggle to gain acceptance as a leader, due to North Korea’s male-dominated society.

“Yo Jong’s role will likely be limited to a regent at most,” Yoo Ho-yeol, a professor of North Korean studies at Korea University, told Bloomberg News. “Not only the male-dominant leadership, but also ordinary people there would resist a female leader.”

Rumors of Kim Jong Un’s health began to circulate after he was not present at a birthday celebration for his grandfather, Kim Il Sung, on April 15. A Japanese magazine, Shukan Gendai, reported Friday that Kim Jong Un fell to the ground clutching his chest during a visit to the North Korean countryside early in April. The magazine also claims that he had heart surgery afterward, leaving him in a “vegetative state.”

North Korea is an extremely secretive country, and there have been no official reports from Pyongyang regarding Kim’s health. Satellite images released by 38 North, a website dedicated to North Korean studies, showed a train owned by Kim on the country’s east coast.

Kim Jong Un has governed North Korea since 2011, after his father, Kim Jong Il, died of a heart attack. He has ruled as an authoritarian, implementing strict control of the media and putting dissenters in hard labor camps.