The capture of two British men in Syria means all four of the IS fighters in a notorious group nicknamed 'The Beatles' are now accounted for.
American officials revealed on Thursday Alexanda Kotey and El Shafee Elsheikh had been detained by the US-backed Syrian Democratic Forces, following the death of ringleader Mohammed Emwazi in a 2015 drone strike and the imprisonment of Aine Davis in Turkey.
The White House believes the group - nicknamed by prisoners because of their English accents - are responsible for the beheading of more than 27 hostages, and that they have used torture methods including waterboarding and electrocution.
Sky News has taken a closer look at the four west Londoners who left home to fight for Islamic State.
The militant who became known as "Jihadi John" moved from Kuwait to the UK with his family when he was six.
He attended state schools and studied computer science at the University of Westminster before leaving for Syria in 2013, where he would take on his infamous moniker.
Emwazi - described by IS as an "honourable brother" - appeared in a string of IS videos showing the execution of foreign hostages, starting with the beheading of American James Foley in August 2014.
The 27-year-old went on to appear in numerous other clips, including those which showed the execution of British aid workers Alan Henning and David Haines, American journalist Steven Sotloff, and US aid worker Abdul-Rahman Kassig.
Emwazi was last seen in a video showing the execution of Japanese journalist Kenji Goto in January 2015 and was killed in a US strike on 12 November 2015 in the then IS stronghold of Raqqa.
According to senior intelligence officials, Davis was plotting an imminent terrorist attack in Europe when he was arrested on the eve of the Paris atrocity in November 2015.
He was taken into custody by Turkish police at a villa just a couple of hours away from the Turkish city of Istanbul, which officials believe was the likely target, and he has remained behind bars ever since.
Davis is serving a seven-and-a-half year prison sentence for plotting the attack.
Before he went to Syria, Davis had led a life of crime in west London. He grew up in Hammersmith and would go on to become a drug dealer, before eventually converting to Islam and becoming radicalised during his time in jail.
His wife Amal El-Wahabi was jailed for two years in 2014 after being convicted of funding terrorism.
The Old Bailey heard how she had convinced a friend to smuggle €15,380 into Turkey to finance her husband's fighting with IS.
The 34-year-old, from Paddington, was born in London and is said to be a Queens Park Rangers fan.
Described by neighbours as a "reserved, polite boy", Kotey is believed to have attended the Al Manaar mosque in Notting Hill with Emwazi after converting to Islam as a teenager.
He would leave his London life and two children behind to travel to Syria in 2009.
Since becoming a member of IS, the terrorist is believed to have helped recruit other Britons to join the terror group, which has been driven out of its Syrian strongholds, including Raqqa.
According to the US State Department, Kotey acted as a guard for IS and "likely engaged in the group's executions and exceptionally cruel torture methods, including electronic shock and waterboarding".
El Shafee Elsheikh
The 29-year-old came to Britain as a child refugee from Sudan and lived in White City, west London.
Before his transformation into a jihadist, Elsheikh worked as a mechanic and was described by his mother, Maha Elgigouli, as "very clever" and a "nice boy".
His father, Rashid Sidahmed Elsheikh, who worked as a translator in the capital, told The Guardian that his son's radicalisation was "lightning fast".
Like Kotey, the US State Department said he had "earned a reputation for waterboarding, mock executions, and crucifixions" while serving as a jailer for IS.
Before that he had been a member of al Qaeda, joining after travelling to Syria in 2012.
He had a daughter called Maha with a Syrian wife, and his first wife, an Ethopian woman from Canada, had joined them and had a son named after his brother Mahmoud, who died fighting for IS in Iraq last year.