It is possible to say with reasonable certainty that Mosab Hassan Yousef is the eldest son of Sheikh Hassan Yousef, a founder of Hamas and one of its most prominent leaders in the West Bank. We also know that Yousef has denounced Hamas publicly since 2008, when he declared that he had converted to Christianity. He subsequently announced that he had willingly collaborated for a decade with Shin Bet, Israel’s domestic security service, starting in the mid-1990s. Yousef first made this claim in a book published in 2010, Son of Hamas: A Gripping Account of Terror, Betrayal, Political Intrigue, and Unthinkable Choices. He repeats his story, under a calmer title, in The Green Prince, a film that won an audience award at the 2014 Sundance festival and is now going…