“We waited so long that we decided to double up!” the couple said to PEOPLE. “We are very grateful for the blessing of twins.”
In a photo she posted Thursday, Johnson showed off her changing figure at 18 weeks pregnant.
"#tbt first baby bump pic at 18 weeks with Twins!" she captioned the photo. "I've popped quite a bit more now. #throwbackthursday #preggers #twins #nomorewaistline."
Johnson and her Shark Tank investor husband met in 2015 when they were partners on Dancing With the Stars. They married in July 2016, and these upcoming twins will be their first children together.
Herjavec is also a father to three children from a previous marriage, but this will be Johnson's first.
The 41-year-old dancer announced her pregnancy with an ultrasound Monday, showing the fetus giving a thumbs up.
"'It's a thumbs up,'" the mom-to-be wrote alongside the photo.
Photo Credit: Getty / David Livingston