The Hollywood stars are expecting their first child together and will welcome their new addition later this year, a representative for Wood confirmed, reported New York Daily News.
"The couple is thrilled," the representative said.
Wood, 25, denied pregnancy rumors in November when she was photographed wearing a baggy top and touching her stomach but the actress took to Twitter to confirm the happy news this time.
"Remember when I said, 'No baby on the way here,'" Wood tweeted, along with a photo of the classic pregnancy guide, What to Expect When You're Expecting.
"Well, I didn't know there actually was! Thanks for all your warm wishes. We are very happy. I'm gonna be a mama!" she added.
Wood first met Bell, 26, in 2005 when they co-starred in Green Day's 'Wake Me Up When September Ends' music video.
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After breaking up one year later, the pair reunited in the summer of 2011 and got engaged in early 2012.
The two quietly tied the knot in October last year during a private ceremony in California.