In August, North Korea's highest-ranking diplomat became the country's highest-ranking defector.

As Pyongyang's deputy ambassador in London, Thae Yong-ho was the public face of North Korea in England, says Stephen Evans, BBC's Seoul correspondent.

Evans has had a working relationship with Thae for years — but he said the diplomat's sudden defection came as a complete surprise. "North Korean diplomats do not defect!" he said.

On Tuesday, Thae spoke for the first time since his defection to South Korea. In an interview with Evans, Thae's message was clear: he has "no regrets at all" about his decision to turn on North Korea.

"I am very happy, and now my family here is settled down, and everyone in my family thinks that it is the right decision," he told Evans.

Now in Seoul, Thae and his family are under the South Korean government's protection, and he's been sharing information with the intelligence services.

According to the BBC, Thae has relayed to the South Koreans that Pyongyang may have an effective nuclear arsenal a year sooner than many experts had predicted. According to Thae, North Korean leader Kim Jong-un issued a directive to complete nuclear development by the end of 2017.

When Evans, who's based in Seoul, came to London in the past, he would often meet with Thae at the Curry House, which Thae recommended. "We had a journalistic relationship," says Evans. "I quite liked him. But he would never crack. No North Korean ever cracks if you go anywhere near a criticism of the regime."

Thae would talk to "left-wing groups about North Korea and how marvelous socialism was," Evans recalled.

And yet Thae seemed very comfortable living as a diplomat in London. "He seemed very English in lots of ways; there's a slight hint of an English accent when he speaks. His kids were educated in public schools and his youngest son is a bright kid ... who was about to go to university."

That probably played a part in Thae's decision to defect, says Evans. The options were sending Thae's son to a great university in England or to a "very limited university in Pyongyang with a very limited future."

Evans says Thae had a message he wanted the North Korean people to understand: "'If the head gets cut off, North Koreans don't get cut off as well." In other words, taking down Kim won't hurt North Koreans — they shouldn't be afraid to be disloyal.

North Korea's response to Thae's defection and statements? "'Human scum' is the phrase that is being used," says Evans. “There’s no doubt that if North Korea could bump off Thae, they would."