Mehdi Hassan, 19, who went by the name of Abu Dujana in Syria, had left the UK with a group of five other Brits to join the jihad.
His family have released a statement saying he had a “good heart” and was trying to “help Syrians”.
They say they had no idea he had intended to go to Syria.
Britons in Syria
Hassan has been due to start at Surrey University before he left. The teenager, who had been privately educated at a Catholic school in Hampshire, had wanted to study International Politics.
Instead, it’s believed he is now the 24th British Muslim to have been killed in the conflict. Research suggests one Brit has been killed in Syria and Iraq every three weeks since the conflict began.