The reality TV star reportedly delivered her first child on Thursday morning near Cleveland, where she spends some of her time to be closer to Thompson, a Cleveland Cavaliers center.
Thompson, mother Kris Jenner, sisters Kim and Kourtney Kardashian, as well as best friend Malika Haqq were reportedly by Khloe's side when she gave birth, according to TMZ.
The baby's arrival comes days after the NBA star was allegedly caught cheating while Khloe was pregnant in several videos that have recently surfaced. Footage from a Washington, D.C., night club in October, showed Thompson kissing multiple women, while another shows him getting close to a different woman.
Neither Thompson nor Khloe have responded to the videos.
In mid-March, the couple prepared for their new arrival with a lavishly pink baby shower boasting celebrity guests and, of course, sisters Kourtney, Kim, Kendall Jenner, Kylie Jenner and mother Kris.
Both Kim and Kylie recently welcomed daughters of their own, Chicago and Stormi, as the KarJenner family continues to expand.
"My baby shower was unbelievable, magical, everything I could have dreamed of and more!!!" Khloe shared on her website after the celebration. "We felt so much LOVE from everyone and it is a day I know Tristan and I will never forget. I'm still dreaming."
While sister Kylie has kept private about her new arrival, Khloe has taken fans along with her throughout her pregnancy journey, sharing updates about the baby's gender, her cravings and her fears along the way.
"I've wanted to have a baby for so long. It's just the perfect timing. God always has a plan, and I just wanted to do it on my time and when I felt comfortable to do so," she told Ellen DeGeneres while appearing on DeGeneres' talk show.
The Good American designer had previously struggled with fertility issues during her tumultuous marriage to basketball player Lamar Odom, who has since admitted he carried on multiple affairs during their relationship.
In September 2017, Kardashian confirmed that she was dating Thompson via a Snapchat video. The two have been inseparable ever since, with the NBA player becoming a fixture on the family's reality TV show "Keeping Up with the Kardashians."
"I'm so blessed that Tristan has been beyond supportive! He's helped me overcome any fear or anxiety that I have!" Khloe wrote on her website the month before the cheating scandal. "He's always so reassuring and confident about everything when it comes to our baby."
With a new batch of KarJenner children running around, there's no chance that we'll see the end of the famous family anytime soon.
"I am now so excited my daughter will have forever best friends with Chicago and Stormi!!," Khloe said on a recent episode of the family show. "Thank you Lord for our princess."