North Korean leader Kim Jong Un’s daughter and apparent successor is believed to have a younger sibling, South Korea’s spy agency said on Thursday, offering a more detailed view of the ruling family’s structure.

Seoul’s spy agency has previously said Kim is believed to have three children, but there has been uncertainty about their order of birth.

Kim’s daughter, Kim Ju Ae, was first introduced to the public in 2022 when she accompanied her father to the launch of an intercontinental ballistic missile.

The Kim family has ruled North Korea with an iron grip for decades, and a cult of personality surrounding their “Paektu bloodline” dominates daily life in the diplomatically isolated country.

“The National Intelligence Service currently assesses that Kim Ju Ae is being groomed as the successor and understands she has a younger sibling of unknown gender,” the agency said in a statement.

The NIS added that it was continuing to verify whether Kim Ju Ae has an older brother, but believes that “even if he exists, he is not in a position to become the successor”.

Since 2022, Kim Ju Ae has appeared at a number of major political events with the North Korean leader, including a high-profile visit to Beijing.

North Korean state media have also referred to her as “the beloved child” and a “great person of guidance” — “hyangdo” in Korean — a term typically reserved for top leaders and their successors.