Dozens of western citizens have travelled to Syria by themselves to fight against ISIS in the last few years, but not all have made it out alive.
Today the bodies of two men killed in battle were brought back to the UK.
Jac Holmes and Oliver Hall, both 24, were killed by explosive devices in Raqqa at the end of 2017.
The men were among British volunteers who travelled to Syria to join the Kurdish-led armed group the YPG, to fight against ISIS.
Jac Holmes, from Bournemouth, travelled to Syria three times, where he became the commander of a sniper unit, the BBC reported.
His parents say they couldn't stop him from going.
His father, Peter, described his shock on first discovering what his son was planning to do.
"I opened a drawer and found his flight confirmation. I had to leave the house pretty quick because I was so angry with him," he said.
Mr Holmes said he later came to feel very proud of his son.
"He did it because it was necessary, protecting innocents who couldn't protect themselves."
Jac Holmes was killed by a suicide vest which was left behind after ISIS forces were ousted from Raqqa in October.
Oliver Hall, from Lee-on-the-Solent, Hampshire, was killed in the city in November after travelling to Syria to join the conflict in August.
His mother Jane Lyndon said an improvised device went off as he was making the area safe for civilians to return home.
The fighters' families and Kurds laid flowers on private ambulances carrying the men's coffins when they arrived at Heathrow Airport.
British authorities have repeatedly tried to deter people from travelling to Syria to fight with armed groups.
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