The Magic Mike star made the announcement on his Twitter feed on July 4.
"happy birthday America, more good news, Camila and I are expecting our 3rd child, God bless, just keep livin," he wrote.
McConaughey, 42, wed the 29-year-old Brazilian model and handbag designer last month in a ceremony held at their Austin, Texas home -- not that the bride felt the legalities were necessary.
"We've been living a married life for over six years now," she told ET Canada in March. "We have homes together, we have family together, we have kids, we've built a life together. So, we've been living a married life this whole time."
"A lot of people, sometimes they're so stuck on 'I gotta get married, I gotta get married,'" Alves said. "They forget that the really important thing… is to have a healthy home, a healthy family, a healthy environment for your kids and to have everything going in a good, peaceful way."
The pair already has two children, 4-year-old son Levi and 2-year-old daughter Vida. They started dating in 2007.
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