The couple announced their big news by posting sweet pictures from a photo shoot they had at their home in Scottsdale, AZ, with their one-year-old daughter Alessi, who held both pink and blue cotton candy to represent the genders of her siblings on the way.
"Alessi is getting a baby BROTHER & a baby SISTER," Lauren, 29, captioned the slideshow of photos. "We couldn't be more excited!"
And Arie wrote on his own Instagram page alongside the pictures, "BOY! & GIRL! How did we get so lucky @laurenluyendyk?! So excited to meet the @luyendyktwins."
Arie, 39, also tagged the twins' own Instagram account, which has already racked up an impressive number of followers.
In addition to their adorable cotton-candy gender reveal, Lauren and Arie also posted a video on their YouTube channel which reveals when the pair first found out about their babies' genders.
Prior to the photo shoot, Arie and Lauren opened an envelope from Lauren's ultrasound in the car while sitting in a Chick-fil-A parking lot.
Lauren explained to Arie how everything was good with her pregnancy but she was told the gender with twins is not always 100 percent accurate and what was in the envelope was just a prediction.
"There's a chance with the ultrasound that what we find out here may be different," Lauren said.
Lauren predicted they were going to have two boys or one boy and one girl, and Arie said, "I just don't understand how they don't know [for sure]... My mind is blown how it might not be accurate."
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After Lauren downed a spicy chicken sandwich, the couple opened the envelope together.
"I've been giggling on the inside because I think based on what [the ultrasound technician said] we're having two girls -- or it says that at least. I'm just thinking how tortured Arie is going to be," Lauren said, joking about how Arie would live in a house filled with girls.
"No, it would be sweet for Alessi to have two sisters, but it would be really nice if there was at least one boy in the group," Arie shared.
The spouses, who got married in January 2019, then cheered and shouted when they discovered they're having one girl and one boy.
Lauren started to cry and Arie gushed, "I hope that's true!... That's amazing!"
Lauren added, "That's so cool," and said she could tell Arie felt "so relieved."
"I'm so relieved that there's at least one boy in there," Arie joked. "Oh my gosh, that's so cool... It's so perfect."
"I'm so happy. How could it get any more perfect than that?... I'm just so grateful. We're just so lucky," Lauren gushed.
Arie proposed marriage to Lauren in March 2018 on The Bachelor: After the Final Rose after Season 22 aired on ABC. The couple then moved into their first home together in Phoenix, AZ, in April of that year.
The pair announced they were expecting their first child together in November 2018 and revealed two months later they had a baby girl on the way.
Arie and Lauren tied the knot at Haiku Mill in Maui, Hawaii in January 2019 and then welcomed Alessi on May 29, 2019.
Lauren finished Arie's season of The Bachelor in second place when Arie actually chose Becca Kufrin as his winner and popped the question to her during the Final Rose Ceremony, which aired in March 2018.
But weeks after getting engaged, Arie decided to dump Becca because he claimed he was still in love with Lauren, and so he begged Lauren for a second chance.
After Lauren decided to take Arie back, the couple got engaged live on television and started their life together.