"Hahaha!! Well I guess the cats out the bag," "Amazing" singer Josh wrote on Instagram following the news. "We're so excited people!!! What an awesome journey !!! Can't wait to hold this little nugget."
The couple already has two daughters: 7-year old Naleigh Moon, adopted from South Korea in 2009, and 4-year-old Adelaide Marie Hope, adopted from within the United States in 2012.
By getting pregnant after adopting, former "Grey's Anatomy" actress Katie is mimicking her own family dynamic, since her sister Margaret was adopted from Korea three years before her parents decided to have her the biological way.
Married since 2007, Katherine and Josh aren't the first Hollywood couple to have a mixed family of both adopted and biological children. Check out 9 more celebs who've done the same:
1. Angelina Jolie Pitt and Brad Pitt: This power couple may be the most well known for having a mixed family of six. Maddox was adopted first from Cambodia in 2002, then Zahara from Ethiopia in 2005, followed by Pax from Vietnam in 2007. But in between, they biologically had their daughter Shiloh in 2006, and twins Knox and Vivienne in 2008.
2. Madonna: The pop star decided to adopt her son David Banda from Malawi in 2008 and returned the following year to adopt her daughter Mercy. But, she already have two biological children from other relationships: Lourdes Leon and Rocco Ritchie.
3. Cate Blanchett: The "Blue Jasmine" actress and her screenwriter hubby Andrew Upton already had three biological boys together before adopting: Dashiell, Roman and Ignatius. But in February 2015, they decided to add to their brood by adopting a little girl named Edith.
4. Denise Richards: The "Wild Things" actress has two adorable daughters, Sam and Lola, from her marriage to Charlie Sheen. But, the currently single mom decided to add to her brood in 2011, when she adopted Eloise Joni from within the United States.
5. Mariska Hargitay: The "Law and Order: SVU" actress and her husband Peter Herman welcomed their son August in 2006, but decided to add to their family with adoption years later. In 2011, the couple adopted a girl and a boy back to back: Amaya and Andrew.
6. Mary-Louise Parker: In 2007, the "Weeds" actress adopted her daughter Caroline from Africa on her own. She already had an older son named William from her past relationship with actor Billy Crudup.
7. Meg Ryan: The "You've Got Mail" actress and her ex-husband Dennis Quaid have a son together named Jack. But in 2006, the single mom decided to add to her family solo when she adopted Daisy True from China.
8. Ewan McGregor: Married since 1995, the "A Million Way to Die in the West" star and his wife Eve Mavrakis welcomed two daughters naturally: Clara and Esther. Then, in 2001, they adopted their third daughter Jamyan from Mongolia, and in 2011, again adopted another girl named Anouk.
9. Tom Cruise: The "Mission Impossible" actor adopted two kids when he was married to Nicole Kidman in the '90s: Connor and Isabella. But he and Katie Holmes, married in 2006, welcomed biological child Suri the same year.
No matter what, it's great to know that children in need of loving families are getting what they deserve.