Why did my brother become an extreme Islamist?
It was in a national newspaper that my step-brother Richard's transformation into an extreme Islamist called Salahuddin was revealed to me.
The article was about "the most dangerous man in Britain", Anjem Choudary. He was the leader of the now banned Islam4UK, an extremist Islamist group intent on implementing Sharia law across the UK.
A few paragraphs down was Richard's name and that of our hometown, Weymouth, in Dorset.
Apparently he was Mr Choudary's newest protege.
He had chosen his new name carefully, and its irony is chillingly revealing.
Salahuddin was a 12th Century Muslim sultan who drove the crusading King Richard the Lionheart - a title Rich had embraced during his childhood - out of Jerusalem.
Of course I could not quite believe it. Who could?
Our parents married in 1992 and we grew up together in Dorset. Richard moved to London five years ago and the family began to grow apart.
But only in 2008 we spent two weeks sharing a room on a family holiday to Cyprus, playing volleyball on the beach.
And now a year later he was in a national newspaper talking of his willingness to fight and die overseas for the Islamist cause.
Our family was devastated. No-one knew anything - it was a huge, ominous unknown. I decided there and then that I would make a documentary, as my way of tackling the situation.
I suppose I remained in a state of disbelief, or denial, until the moment I met with him a few weeks later.
I travelled up from Weymouth and met him outside an east London tube station.
Rich was dressed in an Islamic robe and sported a surprisingly well-developed beard.
"You see all this filth, all this munkar, it will all be gone when the Sharia comes in," he remarked, scanning disdainfully around him.
By "munkar" he meant sin, evil. He was disgusted by what surrounded him.
We walked back to his flat where for five hours he talked about Sharia law, hell-fire and how the majority of Muslims were misled. I left on the train home convinced he had been brainwashed.
A question I repeatedly asked myself was how had it happened and why?
It is a question I still find difficult to answer. Rich has never revealed to me a single moment when he decided to take a right turn, and we both had relatively normal childhoods.
Like many people, Rich left his hometown in search of something more - a purpose and meaning to life, something he found in an extreme brand of religion.
Many of these people are looking for transformations, which is precisely what Islamism demands and provides - Rich to Salahuddin.
The sense of disillusionment in Western society was widely apparent among Rich and his "brothers".
Abdul Dean, another white man, who was once a drum and bass MC, became a Muslim after his sister died of a cocaine overdose aged 18, while Zacariah, once a musician and called Charles, could not relate to former US President George W Bush and the response to the 11 September attacks.
He said: "Basically what spurred me into reading about Islam was George Bush, funnily enough. He said you're either with us or not. And I thought I'm not with him."
When I first began making the documentary and set out on my journey, I expected suspicion, hostility and coldness from those within Rich's group.
They were, after all, brainwashed, hate-filled, crazy people, as often portrayed in the media.
But to my genuine surprise, many of these people were extremely likable, personable and even funny.
It would never be long though before they would be planning another demonstration, where, under the spotlight of the media, these guys would scream: "Murderers" at returning soldiers or burn poppies on Remembrance Day.
It was always a sobering reminder of actually just how far detached from normal society and just how insensitive they had become.
Rich preached: "You foolish people risking your lives for these degenerate rulers, these people who conspire to misguide you into the hellfire."
To begin with, when Rich had been a Muslim for just a few months, everything was new to him, as it was to me.
He was living in a world of perpetual fear, not fully knowing what he was permitted to do and say and what was forbidden in accordance with strict Islamist rulings.
The relationship with non-Muslims such as myself was one of these grey areas, and I found our relationship to be that of just a formality.
Rich told me: "Allah does say in the Koran, not to take disbelievers as your friends and helpers, because they seek to misguide you."
'Shock and hurt'
Gradually he became more relaxed and we have since enjoyed many moments of laughter together.
But his extremist beliefs are always lurking just beneath the surface.
There were moments of real shock and hurt, such as when Rich told me he wouldn't shake my hand because I was a "dirty kafir [unbeliever]", or when I watched as he and his "brothers" publicly burned the American flag on the anniversary of 9/11.
But since the documentary, there have been moments of real hope too. I recently met Rich after he had been given the rare opportunity of a preview of my film.
His feelings were mixed, but after we had finished talking and I had got back into my car, I noticed he was walking back towards me.
I switched off the engine and got out. He shook my hand. "Sorry about the handshaking thing," he said. "I didn't mean to cause offence."
I drove away with a smile on my face. It was comforting to know that things could change, even if only with a fleeting handshake.