Early on Saturday morning, Mustafa Bali, from the Syrian Democratic Forces, tweeted: "Syrian Democratic Forces declare total elimination of so-called caliphate and %100 territorial defeat of Isis.
"On this unique day, we commemorate thousands of martyrs whose efforts made the victory possible. #SDFDefeatedISIS"
It brings an end to five years of violence at the hand of the extremists who blitzed across vast swathes of Syria, seizing Raqqa, and spread into north and western Iraq, capturing Mosul and even advancing to the edges of Baghdad.
Since then there have been concerted international efforts to destroy the extremists, seeing the fall of the self-proclaimed caliphate that once stretched over an area the size of Britain.
Many Christians fled the region following the IS invasion but some small pockets remain in Syria.
Dr Harry Hagopian, an international lawyer and Middle East consultant to numerous church groups, says it's right that today is celebrated but we shouldn't be fooled into thinking this is the end.
Speaking to Premier, he said: "While you eliminate a physical reality you do not necessarily eliminate the concept from the minds of the peoples who backed this whole Daesh (IS) concept."
Hagopian experts IS to move into "clandestine operations" and has warned believers about celebrating prematurely.
"The Christian communities have suffered the brunt of some of the terror and the pillaging and the murders committed by those terrorists.
"I'm sure that a lot of those Christian communities will be happy but when we talk about Baghouz - I do not think that the Christian communities were directly impacted there - but, given what has happened in Syria over the last few years, they would be happy that this stage has been achieved.
"However, this is far from saying 'mission accomplished' as a former US president said about Iraq."
Meanwhile, It's emerged British forces will not scale-back their presence in Syria and Iraq following the capture of the last remaining IS territory.
Major General Chris Ghika, Deputy Commander of the Global Coalition's joint task force, said the terror organisation is by no means "leaderless or rudderless", despite its loss of physical territory.
But he said he could not predict whether the fall of the physical territory would substantially increase or decrease the terror risk to the UK.
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