Reports indicate the dictator had been to see his former lover sing in a concert just nine days before she was arrested and killed

Kim Jong-un’s ex-girlfriend has been executed by firing squad along with a dozen fellow North Korean musicians charged with violating laws against pornography, according to reports in a respected South Korean newspaper.

The Chosun Ilbo said performers from a well-known orchestra and light music ensemble were arrested on 17 August, accused of filming themselves having sex and then selling copies of the tapes.

While this breached North Korean anti-pornography laws, some of the musicians were also found to have Bibles in their possession and all were treated as political dissidents, according to the newspaper’s unnamed source.

They were executed in public by machine gun fire three days later, reportedly as the rest of the Unhasu Orchestra and Wangjaesan Light Music Band were forced to watch.

In accordance with the country’s rules on guilt by association, their families were then taken away to detention camps, according to the reports.

Among those killed was said to be singer Hyon Song-wol, who reached an international audience when she won a Hungarian competition in 2005 and released the hit single “A Girl In The Saddle Of A Steed” – often mistranslated as “Excellent Horse-Like Lady”.

North Korean leader Kim Jong-un met Ms Hyon a decade ago, and they were reported to have been in a relationship until Kim’s father Kim Jong-il said he disapproved.

The South Korean reports included images showing the dictator attending a concert given by Ms Hyon and the groups on 8 August in Pyongyang, and there have been rumours that the couple continued their affair after both married other people.

The paper said Kim's current wife Ri Sol-ju was also a member of the Unhasu Orchestra before she married him. It said: “Whether she had any hand in the executions is unclear.”

Quotations from another source, again unnamed, indicated that the executions on 20 August were in keeping with the dictator’s recent activities, and “show that he is fixated on consolidating his leadership”. The source said: “Kim Jong-un has been viciously eliminating anyone who he deems a challenge to his authority.”

While it is often impossible to verify reports coming out of the closed-off communist state, an authority on North Korean affairs and professor at Tokyo’s Waseda University told the Daily Telegraph there seemed to be “a political reason” behind the killings.

Toshimitsu Shigemura told the paper: “If these people had only made pornographic videos, then it is simply not believable that their punishment was execution.

“They could have been made to disappear into the prison system there instead.

“There is a political reason behind this. Or, as Kim's wife once belonged to the same group, it is possible that these executions are more about Kim's wife,” he said.