SEOUL - Two years ago, Thae Yong Ho, North Korea's former deputy ambassador in London, received an unexpected phone call from the ruling Workers' Party Central Committee in Pyongyang telling him to get ready to receive a very important e-mail.
"Please go to the Albert Hall and buy four tickets," said the cryptic message from a disposable e-mail address designed to throw off Western intelligence agencies.
But the message wasn't code - Thae found out later he was being asked to take leader Kim Jong Un's brother to an Eric Clapton concert.
After receiving the e-mail, Thae said he searched online for upcoming gigs at London's Royal Albert Hall.
One caught his eye: "Eric Clapton's 70th Birthday Celebration Tour".
"I realised, 'Ah! It must be Kim Jong Chol! In North Korea who else would be interested but Kim Jong Chol?'".
Not much is known about Kim Jong Chol, the elder brother of North Korean leader Kim Jong Un, except his love for the music of British guitarist Eric Clapton.
Thae, who defected from North Korea to the South last year, said he was charged with escorting Kim around London when he arrived for the concert.
In an interview in Seoul on Friday, he described the then 35-year-old as a polite young man who said little about his life back in Pyongyang or the politics of his brother.
"He's very free," said Thae. "But he's only interested in guitars and music".
Video of Kim at the May, 2015 concert showed him clad in a leather jacket and wearing aviator sunglasses with an unknown woman by his side, believed at the time to have been his girlfriend.
"She's not his girlfriend," said Thae. She was a rhythm guitarist from the "Moranbong Band" - a North Korean pop group formed by Kim Jong Un after he took power.
Just like Clapton, Kim Jong Chol is an accomplished lead guitarist and jams regularly with the woman, Thae said.
In the days leading up to Clapton's birthday concert, Thae took Kim to Denmark Street, a street in London's glitzy West End packed with guitar and musical instrument shops.
Kim Jong Chol tried out various guitars in every single one of those shops, Thae said, before settling on one where he bought an armful of pedals and mixers to take back home to Pyongyang.
"The shop owner didn't know it was Kim Jong Chol," said Thae.
"He let him play for 30 minutes. The shopkeepers of those guitar shops were amazed by his talent".
Curious at the mysterious guitarist riffing before them, Thae said several shopkeepers started to talk to the North Korean leader's brother, prying him excitedly with questions like 'What is your name?' and 'Which band are you in?'.
"He didn't say anything," said Thae.
"He just smiled".