After the first three men were identified as Choukri Ellekhlifi, 22, Fatlum Shalaku, 20, and Muhammad Mehdi Hassan, 19 – the fourth man has now been revealed.
He is Abdullah Hassan, from Woolwich, South East London, according to The Sunday Times.
Hassan was one of 20 men linked to notorious drug gang the Woolwich Boys who traveled to Syria to join ISIS’ so-called caliphate.
That is the highest concentration of terrorists to emerge from a single area of the UK, the reports says.
In May, footage emerged from a Samsung phone which had been passed from one Brit jihadi to another in Syria and Iraq.
The clips, found on a hard drive by anti-ISIS forces, documented the lives of the brainwashed recruits from their initial optimism to their harrowing, blood-soaked finals days.
Hassan is shown firing guns at a shooting range in the terror group’s capital of Raqqa alongside two young men from Sweden and Australia.
The Brit then turns to the camera and, in a strong London accent, talks about murdering Western soldiers.
He said: “We are going to wed our bullets with the Americans and the British, inshallah [God willing].”
"These bullets will be wedded with your bodies. Americans, British, French ... we are here. Allah will give us victory."
Hassan, also known as Adbi, appeared to have a happy childhood growing up in Woolwich, reports The Sunday Times.
It is unclear whether he was born in the UK or came over as a child with his parents who were refugees from Somalia.
His Facebook profile shows he had normal interests for a young Brit including liking TV comedy shows such as Only Fools and Horses and Never Mind the Buzzcocks.
In 2013, his life is believed to have taken a sinister turn after he reportedly fell in with the infamous drugs gang in the area.
That same year, Fusilier Lee Rigby was murdered near a London army barracks by two deranged militants– one of whom, Michael Adebowale, was linked to the Woolwich Boys.
The gang, which has previously boasted 300 members, was targeted by Islamic hate preachers seeking to corrupt vulnerable young criminals in the city.
One ex-member, who did not want to be named, said the brainwashed gangsters were made to feel part of a “brotherhood” by the men who groomed them for militancy.
Speaking in a video by ConnectFutures, a deradicalization group, he said: "We were extreme in the streets, and when I came to the religion [Islam] we just went from one extreme to another."
The reformed criminal, who now helps young people, said he knew of 16 men from Woolwich who traveled to the Middle East to fight for ISIS.
He added: "Every single one of them died."
Police believe as many as 20 men from the area traveled to the war zone, ConnectFutures says.
Hassan traveled to Syria in early 2015 and is believed to have died within six months of joining the caliphate.
On February 3 of that year, he changed his Facebook profile picture to an image of him wearing Islamic robes along with a cover photo of a mosque in Mosul, Iraq.
According to the Sunday Times, the firing range video was filmed that month.
Locals in a barber shop in Woolwich, where Hassan used to get his hair cut, said news of his death shocked the community.
One said: “We heard that he died not long after arriving in Syria.
"It's still a shock. He seemed a nice guy; very quiet and under the radar not the type of person who would do something like this."
