Thae Yong-ho, former North Korean deputy ambassador to the United Kingdom, defected to South Korea with his family in 2016. They have been under the protection of the South Korean government. (Jun Michael Park/For The Washington Post)

The diplomat’s decision to defect from a regime he had spent his whole life defending did not happen overnight.

Instead, his misgivings had been simmering for two decades, even as he went around Europe espousing the superiority of the North Korean system. They finally reached a boiling point when Thae Yong-ho realized that this regime, to which he had been so loyal, expected him to lie to his children.

“I’ve known that there was no future for North Korea for a long time,” Thae told The Washington Post in his first interview with the foreign media since his escape from the North Korean Embassy in London, where he served as deputy ambassador.

But last summer, he realized his hopes had been misplaced that supreme leader Kim Jong Un, who was educated in Switzerland and is only 33, would turn out to be a reformer. Thae fled, together with his wife and his two sons, now ages 19 and 26.

“Kim Jong Un is still young,” Thae said. “I was afraid that even my grandsons would have to live under this system. I decided that if I didn’t cut the chains of slavery off [my sons], they would complain, ‘Why didn’t you let us be free?’ ”

Thae is the highest ranking diplomat to defect from North Korea. After several months being debriefed by the South Korean intelligence service, he was in Seoul speaking out against the regime’s “reign of terror.”

Over the past month, Thae has predicted to South Korean media the demise of North Korea with the same fervor with which he once extolled its glories. His hard-line statements happen to fit nicely with the hawkish stance taken by the South Korean government over the past eight years. But Thae said he was not being expedient and was speaking his real mind — and was intent on using his influence for good.

“Everyone knows about my defection. Just staying at home or living a quiet life would not effect any change in North Korea,” Thae, a genial 54-year-old who speaks impeccable English, said during an interview in a hotel here.

South Korean authorities are concerned about Thae’s safety and the possibility of an attempt on his life. North Korea released a tirade against him after his defection, calling him “human scum” and a “criminal,” and has made attempts — once successfully — on the lives of other high-profile defectors. Thae was accompanied by an entourage of bodyguards and intelligence officials to the interview.

Time for a ‘Korean Spring’

He spent more than two hours describing his disappointment with Kim, his fears for his children, and his conviction that giving North Koreans information about the outside world would help sow the seeds of dissent — just as it had for him and his family.

“The regime can only stay in place by preventing outside information,” he said. “People there are not educated about the outside world and have no opportunity to experience freedom or a system that is different.”

In North Korea, the Internet is banned for all but a handful of elites, radios and televisions play only state propaganda, and the newspapers are full of the leader’s “great feats.” South Korean dramas are increasingly being smuggled into North Korea, but people watch them in secret, fearing severe punishment if they are caught.

Thae said that anything to break the information blockade in North Korea should be encouraged, from USB drives containing foreign films to radios that can be tuned to news broadcasts from abroad.

“I would like to make it possible for people to rise up,” he said. “We should educate the North Korean people so that they can have their own ‘Korean Spring.’”

Thae’s grandfather and father were devoted to the Kim dynasty, and Thae grew up knowing only North Korea’s peculiar brand of communist personality cult. Then in the 1990s, as a relatively young diplomat, he was posted to Denmark, where his younger son was born, and after that to Sweden.

In Scandinavia, home to the flagbearers of European socialism, Thae’s eyes began to open.

“During my first foreign posting in Denmark, I came to doubt and question whether North Korea could say that it was a true socialist or communist system,” he said. Thae’s time there coincided with a devastating famine in North Korea that killed as many as 3 million people.

“North Korean society doesn’t have the concept of comparing,” he said. “The more time you spend in the outside world, the disbelief in your system grows more and more.”

Doubts about the supreme leader

Thae then did two stints in the embassy in London, first between 2004 and 2008, then from 2013 until his defection last summer. It was during this second stint in London, in the second year of Kim Jong Un’s regime, that Thae’s concerns started to become unbearable.

“Not only me but other North Korean elites were hopeful that because Kim Jong Un had studied abroad and was young, he might change the policy direction and modernize North Korea,” he said.

But Kim soon showed his intention to continue his father’s pursuit of nuclear weapons and his reluctance to introduce the economic reforms the impoverished country badly needs.

“Kim Jong Un made it very clear that North Korea should complete the path toward nuclear development,” Thae said. “This kind of policy is regarded by most North Korean elites like me as very fanatical because it pushes North Korea into a corner of self-destruction.”

The doubts heightened after Kim had his uncle, Jang Song Thaek, executed at the end of 2013. Although executions are not rare in North Korea, there was something disturbingly arbitrary about this one, Thae said.

Still, he continued his duties in London, voicing the idea that North Korea was a “people’s paradise” with free housing, health care and education.

But at home, Thae’s younger son, who was still in high school and hoped to study computer science at a top London university, was asking why North Korea doesn’t allow the Internet, why North Koreans are not allowed to watch foreign films, why North Koreans can’t read any books they want.

“As a father, it was hard for me to tell lies, and it started a debate within the family,” Thae said. “This North Korean system is a really inhuman system. It even abuses the love between parents and their children.”

So, last July, after much preparation and as the end of his posting was approaching, Thae escaped with his wife and both their sons.

Thae declined to discuss the specifics of how his family fled, saying that giving away details could close off the escape route for other North Korean officials abroad.

‘Shame’ over previous role

His arrival in South Korea was the most high profile of what is said to be a string of elite defections. Last year, the government in Seoul hinted that there had been numerous defections from the military and diplomatic service, as well as among officials charged with raising money for Kim himself.

The South Korean government, and some analysts, have portrayed the defections as signs of cracks in Kim’s regime, which has endured despite repeated predictions of its imminent collapse. A former intelligence official told The Post that about 100 elite defectors have been debriefed at a secret residential center run by the government.

“There is no sense of solidarity or loyalty between Kim Jong Un and senior officials,” Thae said. “Senior officials know that this system can’t continue.”

Still, Thae described feeling “shame” about his previous role, saying he was an actor who “pretended to love the system.”

Now, he is trying to fix that. “I’ve decided to spend the rest of my life meaningfully and I want to do something significant not just for my family but also my country.”