His mother Sally, 57, was 'devastated and relieved' upon hearing the news

The mother of deceased British jihadi Thomas Evans has told of how her 'shy and gentle boy' turned into the monster who 'murdered Christians and torched churches'.

Evans left his home in High Wycombe, Buckinghamshire, in 2011 to fight alongside the al-Shabaab terror group in Somalia.

Evans - known as the White Beast for his ruthlessness on the battlefield - became the first British extremist to be killed on Kenyan soil this June after he was shot down during a failed ambush on an army base.

In an interview with Richard Kerbaj for the Sunday Times, his mother Sally, 57, said she was 'both devastated and relieved' when she read of his death on Twitter - and believes he is 'burning in hell' for his crimes.

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Gone: The mother of deceased British jihadi Thomas Evans (pictured) has told of how her 'shy and gentle boy' turned into the monster who 'murdered Christians and torched churches'

Conflicted: Sally, 57, said she was 'both devastated and relieved' when she read about his death on Twitter

Proof: Evans' brother Michael found the picture of his corpse alongside other al-Shabaab extremists (pictured) after a journalist called Sally to ask if she had heard the rumours of his death

Radicalised: Sally Evans has told of how her once-thoughtful son transformed into a feared jihadi known as the White Beast, because of his ruthlessness on the battlefield

Sally painted the picture of a thoughtful boy who, after his father left home when he was 13, assured her that he would never abandon her.

She became suspicious when, at 14, he grew his hair to shoulder-length, began listening to heavy metal music, and started drinking and smoking cannabis with his schoolmates.

She believes his transformation into a terrorist began when he met some new Asian friends at a gym, around the time he broke up with his long-term girlfriend 'who he still loved'.

Thomas changed his name to Abdul Hakim and started using different pots and pans to his family - saying they were contaminated with food that was not halal.

Sally said: 'I respected his right to be a Muslim... but eventually he stopped respecting my right to be secular and repeatedly told his brother and I we were destined for hell unless we converted to Islam.'

She and her other son Michael were confused as at how Thomas, who used racist slurs to describe High Wycombe's sprawling Asian community, became interested in Islam.

'He almost went from one extreme to another,' said Michael.

Evans was stopped by counter-terror police when he tried to board a plane to Kenya in 2011 but four months later, he successfully flew to Egypt. In January 2012, he rang his mother to tell her he had sneaked into Somalia.

In another phonecall with his worried mother, he told her that he had married a young girl who was '13 or 14' and did not speak English.

Firefight: Evans was killed while filming an al-Shabaab raid on a Kenyan military base (pictured)

Transformation into terror: Sally was horrified that her son, who once made mudpies in their back garden, thought it was okay to 'murder innocent men, women and children out shopping'.

'He gave her family an old cow so he could marry her. But at least he's happy. I wish I could say the same, but I can't. I'm heartbroken for him and for this young girl,' Sally Evans wrote in her diary on Christmas Eve 2012.

During another phonecall, she and Evans argued about the Westgate shopping mall attack in Kenya where al-Shabaab terrorists gunned down more than 60 people.

She was horrified that her son, who once made mudpies in their back garden, thought it was okay to 'murder innocent men, women and children out shopping'.

In January this year, she received a phonecall from Evans' wife Sudea who asked for money. She refused on the grounds that she did not want to be seen to support terrorism.

On June 14, Sally received a phonecall from a journalist asking if she had heard the rumours that her son has been killed in battle.

His brother Michael found a picture on Twitter that showed his corpse, alongside those of his fellow al-Shabaab fighters.

Since then, Sally has heard countless stories of the atrocities carried out by her son. One witness from south-east Kenya told of how a 'white man' slaughtered a man with his 'big knife' and another told of how Evans was looking for non-Muslims to kill.

When Sally called Sudea to see how she was dealing with his death, she was shocked to hear he say she was 'happy' because he 'died a martyr fighting for what he believes in'.

At an event organised by the counter-terrorism think-tank Quilliam, Sally said: 'Imagine discovering the death of your child on Twitter and being both devastated and relieved at the same time.