The South's National Intelligence Service (NIS) told a parliamentary committee on Tuesday that it believed Kim's uncle and political regent Jang Song-Thaek had been removed and two associates executed.
Now Jang's nephew, Jang Yong-Chol, the North Korean ambassador to Malaysia, is believed to have been called back to Pyongyang, an intelligence source in Bejing told Yonhap news agency.
The ambassador's wife and two sons were spotted today before boarding an Air Koryo flight to Pyongyang in China's northeastern city of Shenyang, Yonhap said, citing multiple witnesses.
Jang Song-Thaek's apparent dismissal is particularly noteworthy given the crucial role he was seen as having played in securing Kim's own succession after his father Kim Jong-Il's death.
The NIS assessment triggered a wave of conjecture as to why Kim had turned on the 67-year-old who helped put him on the throne, and what it said about the young leader's grip on power.
However, the NIS report was only an assessment, and the main question regarding Jang's dismissal is still whether it actually happened or not.