Kim Ju Ae - who is believed to be 13 - has in recent months been pictured beside her father in high-profile events like a visit to Beijing in September, her first known trip abroad. The National Intelligence Service (NIS) said it took a "range of circumstances" into account including her increasingly prominent public presence at official events" in making this assessment. The NIS also said it would keep close tabs on whether she will attend the North's party congress later this month - its largest political event that is held once every five years.

The party Congress is where Pyongyang is expected to give more details about priorities like foreign policy, war planning and nuclear ambitions for the next five years. On Thursday lawmaker Lee Seong-kwen told reporters that Ju Ae, who was previously described by the NIS as being "trained" to be a successor, was now at the stage of "successor designation".

"As Kim Ju Ae has shown her presence at various events, including the founding anniversary of the Korean People's Army and her visit to the Kumsusan Palace of the Sun, and signs have been detected of her voicing her opinion on certain state policies, the NIS believes she has now entered the stage of being designated as successor," Lee said. Ju Ae is the only known child of Kim Jong Un and his wife, Ri Sol Ju. The NIS believes Kim Jong Un has an older son, but this son has never been acknowledged nor shown on North Korean media. (BBC)