Jac Holmes, 24, is thought to have died while clearing landmines so that civilians could leave the war-torn city, previously the terrorist group’s de facto capital.
The Brit was one of the longest serving volunteers with Syria’s Kurdish People’s Protection Units (YPG), and travelled to Syria three times since 2015.
His mother Angie Blannin said Holmes, who had no previous military experience, had been a “hero in my eyes”.
“He stuck by his convictions because he wanted to be there and he wanted to see the end of Raqqa and to see the end of the caliphate. That was a moment in history, and he wanted to be part of it,” she said to the BBC.
She told the Guardian: “I’m completely heartbroken. I can’t believe he’s gone. I was on the phone to Jac only on Sunday and we talked about how he planned to come home for Christmas now Raqqa is liberated.
— Jake Hanrahan (@Jake_Hanrahan) October 24, 2017
“Everyone who knew him said he was good at what he did. His Kurdish is fluent. I think he had a lot of guys had a lot of respect for him – the Kurds, the westerners, everyone.
“Fighting Isis in Syria was his calling,” she said.
“He was lost for a while before he went to Syria and didn’t know what he wanted to do. He didn’t feel like he had any purpose. This gave him a purpose. He said: ‘Mum, I love what I’m doing and I’m good at it.’ I always respected that and supported him.
“Even though I didn’t want him to go, and we talked about it a lot, you have to let your children grow and be their own person. He was very like me: headstrong. He didn’t like being told what to do,” she said.
Isis faces an existentialist threat after it was defeated in its stronghold of Raqqa.
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Syrian Democratic forces, a group comprised of Kurdish and Arab militias and backed by the US, drove out Isis fighters after battling in the city since June.
The forces raised a victory flag inside Raqqa stadium last week as the months-long battle came to a close.
War monitoring group the Syrian Observatory for Human Rights said Isis was now completely cleared from the city.
In July, Brito Luke Rutter, 22, from Birkenhead, died in an attack on Raqqa, in which American Robert Grodt and Nicholas Warden were also killed.
Ryan Lock, 20, from Chichester, West Sussex, died in December in the same city.
His father, Jon, said in a statement: “Ryan was a very caring and loving boy who would do any thing to help anyone. He had a heart of gold.”
In August, Dean Carl Evans, a 22-year-old from Reading, died alongside Kurdish militia fighters who were trying to take back the city of Manbij, Syria from Isis.