A suspected member of Jihadi John's British execution gang was captured attempting to smuggle himself into Turkey, and eventually back to Europe, a Kurdish militia source has told ITV News.
Alexanda Kotey from west London, was arrested in Syria last month, the source with the mainly Kurdish People's Protection Units (YPG) said.
El Shafee's brother Mahmoud died fighting for so-called Islamic State in Iraq in 2015 after following his brother to the region. On Friday, his parents refused to comment on their son's detention.
"This is not the right time for us," El Shafee's father Rashid said. "This is a mum who lost two. Her son now is in the hands of people, we don’t know what is going on."
The pair were thought to be the two remaining members of the gang still at large.
They may be prosecuted in Syria but it is more likely they will go the United States and possibly the Guantanamo Bay detention camp.
As the so-called Islamic State terror group comes under pressure in Iraq and Syria, thousands of foreign fighters have attempted to flee, but the YPG source did not suggest Kotey was a defector.
Alongside Jihadi John, whose real name was Mohammed Emwazi, and another militant named Aine Davis, Kotey and his friend Elsheikh allegedly formed a four-man IS gang that carried out a series of bloody executions.
Among their victims was the British aid worker David Haines, who was taken captive by IS in Syria in 2013 and later beheaded, apparently by Emwazi.
The four became known as "The Beatles", because of their English accents.
All of them, it transpired, had lived and grown up in West London. Kotey was from Paddington.
Last year the US State Department named Kotey a Specially Designated Global Terrorist, claiming that he "likely engaged in the group's executions and exceptionally cruel torture methods, including electronic shock and waterboarding".
Emwazi, who appeared in horrific videos showing the beheading of British and American hostages, was killed in a British drone strike in 2015.
Davis is in custody in Turkey, where he was convicted on terrorism charges.
Emwazi is also believed to have killed another British captive, Alan Henning, and the American journalists James Foley and Steven Sotloff.
Foley's mother Diane told ITV News that Kotey and Elsheikh's detention was "a positive development".
“My hope is they will be brought to trial and face the consequences of their horrific actions," she said.
"I feel it's very important they are detained and held because they have caused so much pain to so many good people in the world.
"We cannot bring Jim back but we can find justice and hopefully stop this horror that they have inflicted on the world."
Mr Haines' daughter Bethany welcomed reports of the capture of Kotey and Elsheikh.
"It’s brilliant that these evil people have been caught," she told ITV News.
"The families will now have people to hold account for their loved ones' deaths.
"No punishment is enough for these barbarians and in my opinion they should be sentenced to a slow painful death.
"It’s horrible to know that these people will never feel remorse for their crimes but hopefully some justice will be served."
The US government has attributed 27 beheadings to the group.