Since its foundation, North Korea has been ruled by three generations of the Kim family. Its citizens are told that the family hails from a sacred bloodline, meaning only they can lead the country. Kim Jong-Un will want to ensure he passes the mantle down to the fourth generation.But even if Ms Ju-ae is the intended heir, why introduce her so early, and at such speed? Kim Jong-Un is only 39 - his daughter still a child.