The couple are already parents to a 5-year-old son, Gunner.
"Heidi delivered a baby boy at 11:31 a.m. on Thursday, November 17, weighing 7 lb. and 9 oz.," the rep says. "It was an easy birth that took around 45 minutes. Mom and baby are happy and healthy."
Thursday evening, Heidi took to Instagram to share a smiling photo with her new son.
Heidi and Spencer, who already share a 5-year-old son, Gunner, announced they were expecting their second baby in June.
"I have been hoping and praying for this moment for so long! 💕" Heidi, 36, wrote at the time. "Once I saw the word 'pregnant' I started hysterically crying, overwhelmed with joy and shock and I sprinted upstairs to show Spencer."
In July, Heidi and Spencer exclusively revealed to ET that they were having a second baby boy, despite what they'd originally predicted.
"I thought it was a girl. I did, I really did," Heidi told ET. "My whole intuition is off. Gunner is so excited. He kept asking me for a baby before I got pregnant and that made it so much harder."
Heidi embraced her second pregnancy, posting lots of bump photos and sharing several stunning maternity photo shoots.
"There is no time like pregnancy," Heidi wrote in September. "It’s been incredibly beautiful and challenging. So excited to hold my sweet angel! #blessed."
Heidi went through 18 months of trying to get pregnant with her second child.
"I felt responsible. It was just really hard to feel like you want something so bad and it's just not possible," Heidi tearfully told ET in July. "There's nothing else I could have done."
In May 2021, ET spoke with Heidi and Spencer about their struggles to get pregnant with a second child, which Spencer partially blamed on the drama of working on The Hills: New Beginnings.
"Usually these shows are a lot -- for us -- more fun to film. This is the most stressful shooting of anything we've done," he said at the time. "I don't think it's anything to do with anything other than Heidi was so stressed out, dealing with more drama from behind the scenes, on camera, so I think that's why we haven't been able to get pregnant."
In August 2021, Heidi documented having a hysteroscopic polypectomy procedure to remove uterine polyps, which are noncancerous growths attached to the inner wall of the uterus that can be associated with infertility, according to Mayo Clinic.