Chrissy made the announcement on social media on Tuesday, posting a video showing off her baby bump and writing in the caption, "It's John's!"
According to a source close to the couple, it's always been Chrissy and John's plan to expand their family.
"They have been planning for this for a long time," an insider told People. "Chrissy is really excited to finally share the news."
The couple, who are already parents to one-year-old Luna, celebrated their fourth wedding anniversary in September.
[Photo: Getty Images]