Kim Yo-jong, the sister of North Korean leader Kim Jong-un, has arrived in South Korea.
She is the first immediate member of the North's ruling family to visit since the 1950-1953 Korean war.
She and Kim Yong Nam, North Korea's ceremonial head of state, are headed to Pyeongchang to attend the opening ceremony of the Winter Olympics.
Ms Kim, who is said to be very close to her brother, was promoted to the North's powerful politburo last year.
She is on a US sanctions list over alleged links to human rights abuses in North Korea.
At the Winter Olympics, both North and South Korea will march under one flag at the opening ceremony.
Alongside 22 athletes, Pyongyang is also sending more than 400 delegates to the games, including a team of cheerleaders and an orchestra.
The sports diplomacy comes at a time of improved relations between the two Koreas, although experts have cautioned that it does not put an end to underlying regional tensions.
The Korean peninsula has been divided since the 1950-53 war and the two sides have never signed a peace treaty.
Ms Kim is thought to be about 30 years old, and is four years younger than her brother.
Her visit is being seen as a sign that Kim Jong-un is serious about improving ties with the South, the BBC's South Korea correspondent Laura Bicker reports.
Some are also speculating that she might be bringing a message from her brother, our correspondent adds.
On Thursday, North Korea held a military parade attended by Kim Jong-un.
This event is usually held in April and the fact it was moved forward, to the eve of the opening ceremony, had been seen as a setback to the warming of ties.
However, the South has announced that its president will meet the North's Olympics delegation on Saturday.