When Trum – Kim Hanoi Summit failed in February, Kim Jong Un got angry. He thought that some of North Korean diplomats worked for the USA. Insanity prevailed on his mind. He ordered the execution of all of nuclear envoys.
Kim Hyok Chol was also executed in March, 2019. Unfortunately, the killing of Chol remained under carpet for around three months.
It is also believed that Kim Jong Un had been told about illicit sexual relationship between Chol and Kim Yo Jong (the younger sister of Kim Jong Un).
Following is the brief wiki and biography of Kim Hyok Chol:
Real Name: Kim Hyok Chol
Relationship Status: Married
Age: 39 Years