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Did George Clooney put a ring on it? One of Hollywood's longtime most-eligible bachelors may no longer be on the market, and only ET has the reasons why.

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Clooney, 52, and his girlfriend, 36-year-old lawyer Amal Alamuddin, were spotted having dinner at Nobu in Malibu Thursday night with friend Cindy Crawford, and multiple sources confirm that they saw Amal showing off a ring to Cindy, the wife of Clooney's business partner Rande Gerber, sparking rumors of an engagement.

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Security was notably tight at the restaurant Thursday night, and actor Edward Norton was reportedly with the group.

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Clooney's rep did not deny an engagement to ET, stating, "I don't comment on my client's personal life."

The couple was first rumored to be dating in October 2013. As reported by ETonline last month, Clooney and Alamuddin showed some PDA snapped by photographers while on a private photographic and observational safari in Tanzania with a few friends.