On Monday, Natalie also posted photos of herself in the hospital, including when her epidural "hit" during her labor and delivery, via Instagram Stories.
Alongside multiple pictures of River, Natalie also gushed via Instagram Stories, "My girl... Sorry, she's actually so perfect."
Natalie also filmed a video of Nick doing the "dad walk" and carrying their newborn out of the hospital as well as a picture of an Italian club she ate -- and seemingly thoroughly enjoyed -- shortly after giving birth.
Nick, a two-time The Bachelorette contestant who also appeared on Bachelor in Paradise, and Natalie, a surgical technician, announced they're expecting their first child together in early August 2023.
"Our biggest dream came true," the pair captioned two black-and-white maternity photos as well as a sonogram image via Instagram on August 8.
Natalie showed off her baby bump in the pictures while wearing a flowy white dress with puffy sleeves.
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Nick and Natalie got engaged in Venice, CA, in January 2023 after three years of dating.
In July, Nick revealed he bought the lake house his grandfather had built in 1965 for his mother so that it will stay in the family.
"[This is now] the place we will make new memories with our kids [one day]. Finally home," The Bachelorette alum shared with his social-media followers.
Natalie also wrote on Nick's Instagram post, "What a JOURNEY this has been!! We will create the most beautiful memories here and our children will get to grow up enjoying the same slice of heaven their dad grew up enjoying."
Given Natalie's bump was already highly noticeable and it had been a well-kept secret for quite some time, the parents-to-be were already aware of the pregnancy at the time of his social-media posting.
Nick and Natalie have been dating for over three years, and Nick told E! News in February 2023 that they're "definitely anxious to get married."
"We definitely didn't get engaged to have a long engagement, so it's been great. It's exciting," he shared at the time, adding, "We just started talking about [the wedding]."
Nick shared how he and Natalie probably won't be having a destination wedding.
"I don't know if our goal is to have the biggest wedding of all time. I think for us, something we've talked about is it's important to involve people who know our relationship and know us. So I think that would be kind of the driving force," Nick said, hinting the pair may get married close to home in California.
And Natalie chimed in, "Also convenience. We want it to be super easy. I have a lot of older, sick family members that I want to come and I don't want anyone having to fly to Mexico. I want it to be easy for everyone."
Nick and Natalie reportedly first became romantically involved in 2019 but attempted to keep their relationship private for more than a year and didn't go public until after widespread reports that they were dating surfaced in January 2021.
Nick and Natalie had been living together prior to Nick proposing marriage, and so their engagement didn't come as a big surprise to fans. The couple had openly talked about the possibility of getting married and having children together for some time.
"We're having those conversations that everyone is scared to have, but they're definitely needed," Natalie said during a joint interview with Nick on the "Call Her Daddy" podcast in June 2022.
"We talk about finances, children, where we want to live, and things like that. We are definitely opening up and talking about those things more. We're not not trying, we're not trying either. We're just living life."
Nick continued his search for love on reality television following his split from Kaitlyn through a stint on Bachelor in Paradise, but when a romance with Jennifer Saviano didn't work out, ABC selected him to star on The Bachelor's 2017 season.
Nick got engaged to Vanessa Grimaldi, who worked as a special education teacher at the time, but their romance kicked off with more challenges than the average The Bachelor couple to come out of the show given Vanessa had been living in Canada and Nick preferred to stay in the United States.
Shortly after getting engaged for the first time, Nick also competed on Dancing with the Stars, which soaked up a lot of his free time and energy.
Nick and Vanessa split in August 2017 and Nick seemingly never entered another serious relationship until Natalie in 2019.
As for Vanessa, she announced her engagement to Canadian businessman Josh Wolfe in August 2020, and the couple got married on August 2021 in their hometown of Montreal, Canada.