Kim Jong-un's sister will visit South Korea to attend the opening ceremony of the Winter Olympics on Friday, Seoul's Unification Ministry has said.
Pyongyang notified Seoul that Kim Yo-jong would be accompanying Kim Yong-nam, North Korea's nominal head of state, along with two other senior officials, the ministry said.
The two other officials are Choe Hwi, the chairman of the National Sports Guidance Committee, and Ri Son-gwon, the head of the North's agency in charge of inter-Korean affairs, according to South Korea's Yonhap News Agency.
The statement was the first confirmation a member of the North's ruling family would be included.
Ms Kim Yo-jong, believed to be 28, was promoted by her brother last year to be an alternate member of the decision-making political bureau of the ruling party's central committee.
Analysts said the move showed that her activities were more substantive and more important than previously thought.
She is now believed to be one of Kim Jong-un's closest confidants.
The siblings were born to the same mother, Ko Yong-hui.
Kim Yo-jong was seen in state media on Tuesday greeting a North Korean art troupe that has since departed for the South to stage performances during the Olympics.
"One of the positives of her visit is that she is someone able to deliver a direct message on behalf of Kim Jong-un", said Shin Beom-chul, a professor at the Korea National Diplomatic Academy in Seoul.
"This raises worries that North Korea likely intends to use this Olympics as a propaganda tool rather than a possible opening to meaningful dialogue with South Korea".
The war-separated rivals are cooperating for a series of conciliatory measures during the Olympics, which Seoul sees as an opportunity to ease tensions with Pyongyang following an extended period of animosity over its nuclear weapons and missiles program.
Sceptics think the North is trying to use the Olympics to weaken United Nations sanctions and pressure against the country, and buy more time to advance its nuclear weapons and missiles program.
The delegation will visit the South for three days starting on Friday.