Panorama: The Jihadis from my schooldays
In 2013, Nasser Muthana left his home in Cardiff to become an IS fighter in Syria.
Months later, his brother Aseel, joined him.
Reporter Olivia Davies went to school and college with the brothers and wants to find out why they abandoned their life in Wales to become extremists in Syria.
In the UK you can watch the full Panorama programme here from 19:35 On Tuesday 25 January.