Katherine Heigl welcomes her first biological child, brother for two daughters

The baby, named Joshua Bishop Kelley Jnr, is the couple's first biological child, after they adopted two daughters, Naleigh, 8, and Adalaide, 4, in 2009 and 2012 respectively.

Heigl, 38, confirmed the news of her first natural pregnancy in a blog posted last June, revealing her daughters were "excited to welcome their sibling into the fold".

"It was totally unexpected but thrilling," the actress wrote on her blog, Those Heavenly Days. "The whole pregnancy thing is new to me but the thrill of having a baby is not."

"We've known for awhile that we wanted to add to our family and frankly didn't really care how we chose to do that. We were considering adoption again, fostering, or pregnancy if possible. Seeing as I have never been pregnant and as my gynecologist reminded me last year, I'm of advanced maternal age, I wasn't sure pregnancy was even in the cards for us. Turns out it was very much in the cards!"

Heigl has been quite vocal over the years about parenthood, revealing that growing up with her adopted older sister Meg, (who is a South Korean native, like Heigl's daughter Naleigh) spurred her decision to pursue adoption.

"We still talk about having biological children as well — I'm not ruling anything out. But my feeling about adoption is, Why not? There's nothing about it that makes it any less meaningful of a relationship in my mind," she told Redbook back in 2010, after adopting Naleigh.

"Adoption has been a part of my life and a part of my family, so it was how I wanted to start. It felt natural and right to me."

Heigl and Kelley, who met in 2005 and tied the knot in December 2007, had celebrated the pending arrival of their newborn with a nature-themed baby shower last year.

In the lead up, the Grey's Anatomy star blogged details about planning the day.

"I headed straight to Pinterest to cultivate a look for the shower that spoke to not only the holidays, but also our mountain home in Utah where the baby will be born," Heigl wrote.

"I loved that my mum involved me and that I got to contribute my ideas. I'm kind of a control freak on occasion… okay, more often than not, so getting to have a voice when it came to the shower was pretty awesome for me!"