AceShowbiz -

Katherine Heigl, 37, and Josh Kelley, 36, are having a new addition to their growing family. The former "Grey's Anatomy" star is pregnant with a baby boy and due to give birth in January. It's her first biological child with her musician husband after eight years of marriage.

"The Kelley clan is thrilled to announce that we are expecting a third addition to our family," they tell PEOPLE. "Naleigh and Adelaide could not be more excited to welcome their new sibling into the fold and Josh and I are overflowing with joy and gratitude."

"This is an incredibly exciting time for us filled with hope, anticipation, and hormones. Well, only I'm filled with hormones, but everyone in the family gets to enjoy them," Heigl jokes. "We couldn't be more excited to be able to finally share this news with our fans and are looking forward to continuing to share the journey with you all. xoxo, Katie and Josh."

Naleigh was adopted by the couple from South Korea in 2009 when she was 9 months old. She was born with a heart defect and had to undergo surgery before moving to the U.S. Three years later, they adopted a second daughter, Adelaide, from the U.S.

Heigl was inspired by her parents to build her own family through adoption. "Josh and I started talking about it before we were even engaged," she told Parent & Child in 2012. "My sister Meg is Korean, and my parents adopted her three years before I was born. I wanted my own family to resemble the one I came from, so I always knew I wanted to adopt from Korea. We have talked about having biological children as well, but we decided to adopt first. I just wanted to be a mom. So however we do that, it's fine with me."