Sheikh Hassan Yousef, a founding member of Hamas and former spokesman for the Islamist group, was released from Israel's Ofer prison on Sunday, according to Palestinian officials.

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Yousef was arrested with one of his five sons in November 2011 for allegedly plotting to establish a Hamas terror cell in the West Bank.

The former Hamas parliamentarian made headlines in 2010 when another of his sons, his eldest, Mosab Hassan Yousef, recounted his experience spying for the Shin Bet in a memoir "Son of Hamas: A Gripping Account of Terror, Betrayal, Political Intrigue, and Unthinkable Choices."

Mosab was the Shin Bet's most important agent inside Hamas from 1997 to 2007.

The Green Prince film poster

The Green Prince film poster

Yousef's release came two days after the movie adaptation of the book, entitled "The Green Prince," was first screened at the Sundance Film Festival.

The movie title refers to the Israeli security agency's nickname for Yousef, named for the color of the Hamas flag and his high-ranking affiliation with the Islamist organization.

Mosab's autobiographical book 'Son of Hamas' (photo credit: courtesy/Tyndale Publishers)

Mosab's autobiographical book 'Son of Hamas' (photo credit: courtesy/Tyndale Publishers)

Following publication of the book, his father publicly denounced Mosab Yousef's activities in a letter smuggled out of prison and published on the Hamas website. The sheikh was serving a six-year sentence at that time.

Mosab Yousef was responsible for preventing numerous suicide bombings during the second intifada.

Information he transmitted to the Israeli security forces also reportedly led to the arrests of prominent Hamas members, including Abdullah Barghouti and Ibrahim Hamid, Hamas commanders in the West Bank, as well as Fatah Tanzim commander Marwan Barghouti. In 2007, Yousef fled to California and subsequently converted to Christianity.

Following his release on Sunday, Hassan Yousef told reporters that he would return to the political limelight to advance reconciliation talks between Fatah and Hamas.

Marwan Barghouti in court in 2002 (photo credit: Flash90)

Marwan Barghouti in court in 2002 (photo credit: Flash90)

Reconciliation negotiations between Fatah and Hamas resumed secretly on January 6, according to the independent Palestinian news agency Ma'an.

The relationship between Fatah and Hamas, longtime political rivals, took a drastic turn for the worse in 2006 after Hamas won parliamentary Palestinian elections and subsequently took over the Gaza Strip by force. Since then, attempts at reconciliation, including a Cairo-brokered agreement in 2011 and another agreement in 2012, did not lead to a unity government between the two parties.