Teenager Lloyd Gunton has been slapped with a life sentence for planning a terror attack at a Justin Bieber concert.

Gunton, 17, reportedly wrote a "martyrdom letter" and researched security for Bieber's gig in Cardiff as part of his planned attack. Police raided the boy's south Wales residence on the day of the concert and they discovered a gutting knife and a claw hammer inside his school backpack.

"I am a soldier of the Islamic State. I have attacked Cardiff today because your government keep on bombing targets in Syria and Iraq. There will be more attacks in the future," his letter read.

During the trial, Birmingham crown court's jurors were told Gunton also had a note with bullet points that include "strike the infidels who oppose Allah in the neck" and "run down the non-believers with a car."

According to The BBC, he had posts in June 2016 that showed support for Al Qaeda. In addition, Gunton — who had been diagnosed with autism — shared photos of the Islamic State's flag. Investigators dug deeper into his online profiles and discovered that the password to his Instagram account was "truck attack."

One of his social media posts even directly pertained to a terror attack, which read, "May Allah bring terrorism to Cardiff on 30th June."

Aside from his disturbing posts, authorities learned that he had researched how to stab and kill, as well as how to carry out an attack by using a vehicle.

The troubled teen was found guilty of one charge of engaging in the preparation of a terrorist act, as well as two charges of possessing terrorist information and two charges of encouraging terrorism. He is required to serve a minimum of 11 years behind bars before being eligible for parole.