Mosab Hassan Yousef, the son of a leading member of Hamas, has revealed himself to be an agent for Israel's security service.
In over a decade as a secret source working within Hamas, he exposed plans to launch suicide bombings and supplied information that led to the arrest of dozens of Hamas terrorists.
The son of Sheikh Hassan Yousef, one of Hamas's founders and the leader of its military wing in the West Bank, Mr Yousef has written a book to appear next week in the United States, titled Son of Hamas.
Mosab Hassan Yousef, 32, left the West Bank three years ago, after secretly converting to Christianity. He lives today in California.
Mr Yousef's code-name in the Shin Bet was "Green Prince", for his pedigree and the colour of Hamas's flag.
He was arrested in 1996, after buying a gun while a member of Hamas's student movement. The Shin Bet asked him to become an informant, and after his release the following year, he began supplying his handlers with valuable information.
In an interview with Ha'aretz, Mr Yousef explained that he co-operated with Israel to save lives, and because he believed that the Shin Bet was working to preserve the ideals of a democratic society, unlike Hamas and Fatah.
Mr Yousef's information was especially crucial during the Second Intifada when it helped the Shin Bet arrest military commanders of Hamas and Fatah, including Fatah-Tanzim leader Marwan Barghouti.
While he was an informant, Mr Yousef ensured that Israel would not assassinate his father, the Sheikh, who was intimately involved with Hamas's terror attacks. The Sheikh was since arrested along with his son, who was subsequently released.
A former Shin Bet agent handler who worked with Mr Yousef told Ha'aretz: "So many people owe him their life and don't even know it." He said that Mr Yousef had worked for the agency without expecting any payment.
Mr Yousef said that he wants his book to send a message of peace, though he is pessimistic about the chances of a peace agreement between Israel and Hamas and Fatah.
"I tell you with certainty that the Israelis care about the Palestinians far more than the Hamas or Fatah leadership does," he said.