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 attending the opening ceremony of the Winter Olympics in Pyeongchang.
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.
Kim Yong-nam has shaken hands with South Korean President Moon Jae-in at a reception dinner for world leaders.
Also present at the event were US Vice-President Mike Pence and Japanese Prime Minister Shinzo Abe.
Mr Pence had been due to sit at the same dinner table as Kim Yong-nam and Mr Moon but left before the meal was served, AFP reported.
At the Winter Olympics, both North and South Korea will march under one flag at the opening ceremony.
Alongside 22 athletes, Pyongyang has sent 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, around 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.
She adds that some are also speculating that Ms Kim might be bringing a message from her brother.
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.