Pyongyang, North Korea - North Korean leader Kim Jong-un is grooming his teenage daughter as his successor, according to South Korean lawmakers briefed by Seoul's spy agency on Monday.

The daughter, Kim Ju-ae, whose age has not been confirmed, has been seen with her father at a variety of events, fuelling speculation that Kim Jong-un has chosen her as heir apparent to lead a fourth generation of hereditary rule by his family.

South Korean MP Lee Seong-kweun said the National Intelligence Service (NIS) has judged that she has been chosen as heir.

"Pyongyang is teaching Kim Ju-ae to be heir apparent, indicating she's the most likely successor," Lee told reporters after the agency briefing.

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The NIS also told parliamentarians that Kim Jong Un is now "heavily overweight" at "around 140 kilograms (308 pounds)", putting him at "high risk of heart-related illness."

Kim, who is widely known to be a cigarette smoker, was said to have shown symptoms of high blood pressure and diabetes in his early 30s, Lee cited the NIS as saying.

North Korea also appears to be adjusting Kim Ju-ae's level of exposure to the public, monitoring how North Koreans react to her role as potential successor, the NIS told MPs. More than half of her outings with her father were related to military activity, such as overseeing drills.

Kim Ju-ae was referred to as a "great person of guidance" – "hyangdo" in Korean – by state media in March, a term typically reserved for top leaders and their successors.

"Considering the word 'hyangdo' was used, which is only reserved for a leader or successor, the NIS is assessing the succession plan is in shape to some extent," Park Sun-won, another MP, told reporters.

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However, Park said the NIS has not ruled out the possibility that another sibling could emerge as a potential alternative in the succession plan, given that North Korea has not made an official succession announcement.

First introduced to the world in 2022, Kim Ju-ae was once thought to be her father's second child. However, Seoul said last year it was "unable to confirm for sure" that a once-suspected older son existed.

Ex-NBA star Dennis Rodman visited North Korea in 2013 and claimed he'd met a baby daughter of Kim's called Ju-ae.