[roywiggins]

Kim Jong Nam, Un's half brother, was assassinated with VX nerve agent. He was exiled to Macau where he was protected by the Chinese government, and speculated to be kept around by the Chinese as a potential puppet leader if they decided to remove Kim Jong Un. Because he was Kim Jong Il's eldest son, he might be an acceptable leader- the juche ideology claims blood descent from gods or something, and he is in the royal lineage.

How likely is it that China approved the assassination, really?

[carlossilva33]

A very good point. Following that train of thought I would usually look at 'who benefits' and be content with thinking some Western country would have been responsable but the assassination method was just very atypical.