The British ISIS terrorist dubbed Jihadi John was killed by U.S. drone after he was given away by his beard and the way he walked, a new documentary claims.

The terrorist, whose real name was Mohammed Emwazi, became the face of the terror group, appearing in multiple propaganda videos where he beheaded innocent people, including Americans and Britons.

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A documentary for British TV station Channel 4, which is airing on Monday, reveals that the extremist met his fate when U.S. forces identified him after a drone flew at night over Raqqa, at that point an ISIS stronghold.

British intelligence apparatus worked tirelessly to identify Emwazi after he first appeared in an ISIS video back in 2014 with American journalist James Foley (pictured) who was beheaded off-camera after reading a prepared statement criticizing the U.S.

British intelligence apparatus worked tirelessly to identify Emwazi after he first appeared in an ISIS video back in 2014 with American journalist James Foley (pictured) who was beheaded off-camera after reading a prepared statement criticizing the U.S. (AP)

Within 15 seconds a missile was launched to wipe out Emwazi. The unsuspecting terrorist was speaking on the phone when the missile hit him, The Sun reported.

Colonel Steve Warren, who was the Pentagon spokesman at the time, told the documentary that because it was dark and they couldn’t see his face, the military identified Emwazi by his beard and the way he walked.

“You can't see his face but we could sort of see how he moved, the cut of his jib, so to speak. The angle of his beard, these things we could see,” he said.

“Eventually we were convinced that this is Jihadi John. And so the floor commander at the time orders, ‘Take the shot.’ Within 15 seconds a missile obliterated Emwazi.”

“Eventually we were convinced that this is Jihadi John. And so the floor commander at the time orders, ‘Take the shot.’ Within 15 seconds a missile obliterated Emwazi.”

— Colonel Steve Warren

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British intelligence apparatus worked tirelessly to identify Emwazi after he first appeared in an ISIS video back in 2014 with American journalist James Foley who was beheaded off-camera after reading a prepared statement criticizing the U.S.

Emwazi was dubbed “John” by a group of hostages, in reference to John Lennon of the Beatles, because the four-man terrorist cell all appeared to have English accents. He was subsequently nicknamed “Jihadi John” by the media.

Emwazi is understood to have taken extensive measures to avoid being detected, including wiping every computer he used to send messages. But despite his best efforts, British intelligence agency GCHQ quickly established his identity after using voice recognition technology and comparing his voice to the recordings from previous wiretaps taken during a surveillance operation.

The intelligence agencies also looked at the pattern of the veins in his left hand and matched it with an archive picture of him.

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“We had a race to find out who he was — his size, his hands, but, above all, his voice, made identifying him quite easy,” Robert Hannigan, a former director of GCHQ, told the Sunday Times.