The parents of a British man accused of being a member of so-called Islamic State say they do not know if their son is dead or alive.
Jack Letts, dubbed "Jihadi Jack", travelled to Syria in 2014 and was later captured by the Kurdish-led YPG.
Speaking for the first time since he was charged, John Letts and Sally Lane told the BBC the last three years had been a "nightmare".
Jack Letts, who was captured in May, has previously said he opposes IS.
A Muslim convert from Oxford, the 21-year-old has been charged with being an IS member by local police force the Asayish.
John Letts and Sally Lane claim he went to Syria for humanitarian reasons, and have not heard from him since July.
Ms Lane said: "We can't conceive of a world where we won't see him again and we can't go there really.
"We have to believe that he's alive and that reason, sense and justice will prevail, because we can't cope otherwise."
Mr Letts said: "It's been three years.
"I remember when I said goodbye to him. Little did we know it would be a nightmare three years."
Kurdish officials have told the BBC they are willing to hand over prisoners of war to their countries of origin, but there had been no official request for Mr Letts.
The couple, who along with their son have dual citizenship, said they had made repeated attempts to get the British or Canadian government to bring Jack home.
Jack Letts has been under investigation by UK police, and may face prosecution if he returns.
John Letts and Sally Lane face charges of funding terrorism for sending Jack money, which they deny.