How an enemy can offer a green light to peace

During the first Gulf War, in fact, Mosab had stood on a roof-top in Ramallah doing just that as Scud missiles flew towards Tel Aviv. And, when the first intifada erupted, he'd hero-worshipped the "masked men" of Hamas who set out to spill Israeli blood. "Mosab wanted to be one of them but he wasn't allowed, ironically, because of his father's position," says Schirman.

I believe that things are going to work out - we share so much

Hate and anger were part of the environment, and Hamas used them "as a political tool". At 17, Mosab was arrested for smuggling guns. After extensive interrogation, he agreed to work for the Shin Bet. He still wanted to kill an Israeli, and secretly plotted to murder Gonen. But after spending time in prison as a ruse to get him closer to Hamas's leaders, and seeing the brutal way that the group dealt with suspected collaborators in its ranks, the Palestinan's moral compass shifted.

Schirman recalls that Mosab had also been shocked by the way that the organisation used civilian children as shields during the second intifada. "He talked to me about violent demonstrations that he would go to where they put children in the first row to go against tanks, because the leaders knew it was good for the media." They even used slogans about building "our pride on the blood of our children".

Mosab explained that, in the process of changing sides, he "chose to be with people who favour life rather than death," says Schirman. "In his environment, you had to die, be a martyr, whereas the Shin Bet wanted him to be alive. For their own aims, but there was a deeper philosophical sense with this, too." Mosab became his father's closest aide and gatekeeper, secretly passing intercepted communications between him and other Hamas leaders to the Shin Bet. He helped thwart terrorist attacks, and saved Israeli and Palestinian lives. His father regarded him as a traitor when he learned the truth. In a story that's riddled with irony, however, he would have been assassinated if Mosab hadn't been working for Israel. Today, they are separated by geography, religion and ideology.

Hassan publicly denounced Mosab for his betrayal, but he had no choice, claims Schirman. "Had his father endorsed him, the whole family would have been killed."

Mosab's love for his family, and his sadness at losing them, is palpable. His experiences with the Shin Bet, however, have expanded his horizons beyond the "very fundamental, very religious environment" in which he was raised, creating a wide divide. "He learned about democracy, he taught himself about different religions, he became a Christian, but in a spiritual way not in a religious way, he learned about Judaism. He took off the blinds," says Schirman, "whereas he knows that his family is very much stuck in that world with the blinds on. That is very frustrating for him and I think he believes that only when they are able to take off the blinds and think freely, will they be able to connect again."

And therein, at least in part, perhaps, lies the secret of a future peace. Most encouraging, though, is the deep and lasting bond of trust that developed between Mosab and Gonen. The latter lost his job over breaking protocols for his charge, and risked being accused of treason, Schirman claims, when he went public with his story for the first time in The Green Prince: a film, ultimately, about humanity triumphing over the seemingly insurmountable differences fuelling the Middle East conflict. "When an Israeli meets a Palestinian, it's all good," says the director. "They share the same sense of humour. They like the same food. They're close. I believe in people and I believe that things are going to work out, somehow. I know that there's nothing on the horizon to indicate this right now, but I think it's going to work out."