Nikki captioned a series of black and white photos from her delivery room at the hospital and wrote, "11-15-22. River Thomas VanLoo made his fashionably late yet very dramatic entrance into the world."
"He managed to give us quite the scare but also might have set the record for shortest NICU admission," she shared. "Riv we couldn't love you any more if we tried, baby boy."
Nikki posted several photos of herself holding her child as well as Tyler admiring his newborn son, who clearly spent some time in the NICU after his birth.
Nikki also gushed about her husband on Instagram Stories, writing, "This guy right here has been the best support, a true teammate, and the best dad. My heart could burst thinking about how lucky I am to have you these last few days."
Tyler commented on his wife's post, "My whole world. I love you so much babe."
And Nikki also received kind and congratulatory messages from some Bachelor Nation alums.
Former The Bachelorette star Andi Dorfman wrote, "Awwwww congrats to you and Tyler!!!! Ahhh he is so perfect! Sending so much love from the instant River fan club!"
Nikki's previous stint on The Bachelor was a tumultuous one.
The nurse and Juan Pablo endured a highly-publicized and criticized relationship following the 2014 finale of The Bachelor, which featured an anti-climactic ending in which Juan Pablo just told Nikki, "I like you."
Instead of proposing marriage to Nikki or at least expressing love, he offered her nothing but his final rose.
Rumors swirled at the time Juan Pablo couldn't communicate his feelings for Nikki and allegedly used her for the fame of their celebrity pairing.
"I knew I was never going to be the No. 1 priority, like, he has a daughter. But I mean, there's a difference between being the second priority and the seventh priority. We're just different people and... we just never saw eye to eye on [things]," Nikki told former The Bachelor franchise host Chris Harrison in January 2015.
"It's not from a lack of trying on either side. I tried really hard and he tried hard too... It's just, I'm a nurse in Kansas City and he lives in Miami, and he's in the entertainment industry... It was just really hard for me to fit into that."
ManyThe Bachelor fans strongly disliked Juan Pablo during his season for how he treated the women, and those negative opinions spilled onto Nikki for choosing to be with him despite those obvious flaws.
"No one prepares you for what's going to happen on the show and being in the spotlight... I wanted everyone [to] be happy for me, and I felt like [our situation] was misunderstood for a lot of reasons... the hurtful things that people said to me, it's just no one can prepare you for that," Nikki added in her interview with Harrison.