Kadiza Sultana, one of three schoolgirls from east London who ran away to join Isis, is thought to have been killed in an air strike in Syria.
Ms Sultana, 17, left Britain to travel to Syria in February 2015 with fellow teenagers Shamima Begum and Amira Abase.
But Ms Sultana’s family, who had been in contact with her by phone, believes she was killed in a Russian bomb strike on Raqqa in May, according to ITV News.
The girls, who attended Bethnal Green Academy in east London, may have been radicalised by Isis propaganda distributed online.
Ms Sultana was 16 when she flew to Istanbul and travelled onwards to the Syrian border with Ms Abase and Ms Begum, who were both 15 at the time.
The trio were feared to have become so-called “jihadi brides”, and Ms Sultana’s husband was an American national of Somali origin who died late last year, according to the Press Association.
Ms Sultana was planning to escape and return to Britain, having become disillusioned with life in Syria, but died earlier this year when her home was destroyed in an air strike.
Her sister, Halima Khanom, gave an interview to ITV News that included clips of phone recordings between the siblings.
Ms Sultana, speaking before her death, said: “I don't have a good feeling. I feel scared... You know the borders are closed right now, so how am I going to get out?”
Her sister asked how confident she was of escaping and she replied: “Zero.”
All three girls were represented by lawyer Tasnime Akunjee, who told ITV News: “You would move heaven and earth to get any child back from a danger zone, and this family had done all they could and stretched every sinew to get their daughter, their sibling back home.
“Perhaps the only benefit out of this is as a tombstone and a testimony for others of the risks of actually going to a warzone, to dissuade people from ever making that choice.”
The lawyer who represented the girls has said: “Leaving Isis is like trying to escape from Alcatraz, with a shoot-to-kill order added in.”
Ms Khanom said: “We were expecting this in a way. But at least we know she is in a better place.”
The Bethnal Green schoolgirls were among more than 800 Britons believed to have left the UK to join Isis or other militant groups in Syria and Iraq, ITV News said. It is thought that at least 250 have since returned.
Some have faced prosecution, with others allowed to re-enter society under the watch of security services.
Metropolitan Police Commissioner Sir Bernard Hogan-Howe had told MPs last year the Bethnal Green trio would be unlikely to be prosecuted if they returned to Britain unless there was evidence they had committed any specific crimes while with Isis.
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