OK! COVER STORY: Sandra Bullock's Hookup With Ryan Reynolds' Best Friend!

Sandra Bullock gave Jonathon Komack Martin her most heartfelt movie star smile as he opened the passenger side door of a white Porsche Panamera for her. The pair were spotted together on Jan. 22 as they arrived together at a private party at an L.A. townhouse.

"Jonathon was very attentive to Sandra," says an event onlooker. "He did't leave her side all afternoon."

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That wouldn't come as a surprise to people who know them. "Sandra and Jonathon are great friends," another insider divulges, adding, "they were introduced years ago and they've always hit it off. She's been spending more time and more time with him, going to parties or just hanging out, and that's got everyone talking."

But Sandra, 47, is tired of answering nosy questions about her personal life and, she's justifiably protective of her date, Jonathon.

"She's being extremely secretive, though, which is typical. And give what she's been through, you can hardly blame her," says the insider. "Even when probed, she won't reveal much more than saying what a great guy Jonathon is."

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Last year, Jonathon was a producer on The Change-Up, which starred Ryan Reynolds — Sandra's co-star in The Proposal and the man who helped her find her smile again after her ugly divorce from Jesse James in 2010. 

Sandra and Ryan, 35, who was fresh from his split from Scarlett Johansson, denied a romance, but the pair spent a lot of time together last summer, and fans and Hollywood insiders hoped that the natural chemistry Sandra and Ryan displayed on screen would travel into real life.

FOR MORE ON SANDRA BULLOCK'S MYSTERY DATE AND HOW HE HAS REPLACED RYAN REYNOLDS, PICK UP THE NEW ISSUE OF OK!, ON SALE THURSDAY!