The North Korean leadership’s days are “numbered” as its people become increasingly disillusioned, a top defector says.

“The traditional structures of the North Korean system are crumbling,” Thae Yong-ho, formerly Pyongyang’s number two diplomat to London, said Wednesday in Seoul, during a news conference for foreign correspondents.

He cited his sons, who were exposed to Western culture and free internet policies when they lived with him during his time in London, saying their constant questioning of the differences between the two governments led him to defect for his family’s sake.

Thae defected to South Korea in August, the most senior North Korean official to defect in almost 20 years. Since then, North Korea has publicly and repeatedly demanded his return, calling him “human scum” and accusing him of embezzlement and espionage.

South Korean officials have used his defection as an example of growing disillusionment among North Koreans.