The ex-girlfriend of North Korea dictator Kim Jong-un has been executed by firing squad for appearing in porn films, according to a South Korea newspaper. Singer Hyon Song-wol is said to have been killed along with a dozen fellow North Korean musicians, just days after North Korea's leader saw her perform in concert. The Chosun Ilbo newspaper 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. An unnamed source told the newspaper some of the musicians were also found to have Bibles in their possession and all were treated as political dissidents. It is reported the rest of the Unhasu Orchestra and Wangjaesan Light Music Band were forced to watch as they were executed in public by machine gun fire three days later. In accordance with the country’s rules on guilt by association, their families were then taken away to detention camps, according to the reports. 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. There have been rumours that the couple, who were both married to other people, were having an affair, and the paper said Kim's current wife, Ri Sol-ju, was also a member of the Unhasu Orchestra before she married him. 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."