Jang Kim Song (also known as Kim Jang Hyun), born in the mid 70’s is an adopted son of Jang Sung Thaek (the probable father is Kim Il Sung, the eternal president of the DPRK), who according to South Korean medias was probably purged in december 2013 (being in connexion with his father). The reality seems to be different. According to a North Korean source, Jang Kim Song is currently living between his house in Pyongyang and the home of his mother Kim Kyung Hee. Jang Kim Song is also highly connected to Kim Jong Nam, another son of Kim Jong Il who is living far from Pyongyang for safety reasons.
Jang Kim Song was educated in Europe with Kim Jong Il’s children. All of them had been educated in Switzerland under the patronage of Ri Su Yong (the current MOFA minister) and by Jang Sung Thaek relatives especially by Jang Song Yop (a brother of Jang Sung Thaek). Jang Kim Song returned to North Korea in the early 90’s and strated to work in political and economical structures of the KWP. In the past he also accompanied his father during trips to China and South Korea (see below probably Jang Kim Song who is encircled in red). I cannot confirm that the encircled in the son of Jang Sung Thaek, however according to a former defector, Jang Kim Song was very often travelling with his father, therefore I imagine that this young person is a relative of the deceased uncle of Kim Jong Eun.