Lauren said she asked Arie to read the results of the home pregnancy test.
"Arie came out with the test in his hand and tears in his eyes. He was like, 'You're pregnant!'" Lauren recalled.
The emotional moment prompted Lauren and Arie to seek confirmation, so the couple apparently drove to a store and bought six additional pregnancy tests.
"Lauren took all of them and they were all positive," Arie revealed. "We weren't trying, but we are so excited. It's going to be a whole new chapter in our lives."
Lauren, who is reportedly pursuing a career in real estate, and Arie, a 37-year-old race car driver, purchased a home together in Phoenix, AZ, in April 2018, just one month after getting engaged on The Bachelor: After the Final Rose special on ABC.
Arie and Lauren -- who share two dogs, Bastain and Dallas -- are reportedly set to tie the knot at the Haiku Mill in Maui, a historical venue reportedly famed for its lush gardens and hanging vines, in January 2019.
While the couple is thrilled about Lauren's pregnancy, the blonde beauty admitted her experience thus far has been tough.
"October was miserable. I had really bad morning sickness and barely left the house," Lauren told the magazine. "But over the last week, I've started feeling a lot better, so it's nice to have my energy back."
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Lauren claimed her husband-to-be "does everything" around the house to help out when she's under the weather, but now that her health has taken a turn for the better, she has hired a personal trainer.
"When I wasn't feeling that great, I was trying to go on a lot of walks. But now I do cycling a few times a week!" Lauren shared.
Although Lauren will have a growing baby bump, she and Arie insisted the wedding is still on and they will exchange vows in January 2019.