The couple is already parents to 1-year-old son Hemingway.
According to Hollingsworth, baby No. 2 was a big "surprise," but he and his wife "couldn't be happier about our growing family."
“We were traveling to Paris for a friend's wedding and then we took a family vacation through Tuscany. As you can imagine, there were some romantic nights and, well, I might have to take responsibility for this one,” he tells ET.
The two are already parents to son Hemingway, who was born in July 2016. "I love Hemingway so much and I couldn't wait to have another," the actor gushes.
The couple is expecting their little one in March, but staying tight-lipped on baby names for now.
See more in the video below.
Reporting by Brendon Geoffrion.