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Joe Manganiello is officially off the market ... he's engaged to longtime girlfriend Caitlin O'Connor , TMZ has confirmed. Getty

Sources close to the couple tell us ... the two are engaged and are excited for this next chapter in their lives. We're told, Joe announced Caitlin as his fiancée at the San Diego Film Festival during his speech last night. He thanked his betrothed for her love and support while accepting his Career Spotlight award.

It's unclear when or where the proposal took place ... but there were engagement rumors back in June when Caitlin was photographed with a large diamond ring on her ring finger on a trip to Italy with Joe. Backgrid

This will mark Caitlin's first marriage and Joe's second. He was previously married to Sofia Vergara for almost 8 y

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