Issam Abuanza, a Palestinian doctor who has British citizenship, left his wife and two children in Sheffield, England, and joined ISIS in July 2014, according to leaked recruitment papers by the terrorist group.
"He used to be quite the dashing young man, very modern," Abuanza's sister, Najla, recently told BBC News. "I've no idea how he became like this or who showed him the path to terror."
"[Our parents] will never forgive him," Najla added. "My dad's wish was to see him before he dies. He has spent all his money on him and his education and this is what he does."
The 37-year-old ISIS member became a doctor in Iraq in 2002, worked at a hospital in Wales from May 2007 to July 2009, and at a hospital in Scarborough, England, from October 2012 to August 2013, notes the International Business Times.
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Issam posted a picture (above) of himself on Facebook dressed in medical scrubs, armed with a gun and pointing his finger in the air, an image often associated with Islamic extremism. Another Facebook picture showed him in military garb, holding a rifle and reading the Quran, reports BBC News.
In addition to pictures, Issam cheered the terrorist attack against the Paris editorial office of Charlie Hebdo on Facebook in January 2015: "Praise be to God for this terrorist act. God kill off their enemies, military and civilian, men and women, adult and children..."
In February, Issam wrote about a Jordanian pilot who had been burned alive by ISIS: "I would've liked for them to burn him extremely slowly and I could treat him so we could torch him once more."
While working as a doctor for ISIS, Issam noted on Facebook: "We get a lot of spinal injuries which cause the paralysis of mujahideens [fighters] because we don't have spinal surgeons."
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Issam has called on doctors to join ISIS and claimed that some have.
It's not known where Issam is currently living and he has not posted on Facebook since October 2015.
His sister slammed him on Facebook for leaving his family to join ISIS: "You left them in the same country which is after you now."