The couple first announced their new son's arrival last week.
The happy parents named their new bundle of joy Rio John Chmerkovskiy, Murgatroyd wrote on Instagram. The news comes just under a week after Chmerkovskiy, 43, and Murgatroyd, 36, announced Rio's arrival on June 18. The couple are also parents to 6-year-old Shai Aleksander.
"We are overjoyed to share our baby boy with all of you," Murgatroyd continued this week. She added that Shai "is already the best big brother and we all feel very complete Life is good XO."
Chmerkovskiy shared the happy news of Rio's arrival last week, with a fitting Father's Day post on Instagram. Holding onto the newborn, whose face the proud dad blurred out, he wrote, "Happy Father’s Day to me! #MadeInPeta."
The couple first broke the news they were expecting again in January.
"It brings me immense joy to finally announce that @maksimc and I are expecting our Chmerkovskiy #2," Murgatroyd captioned her announcement on Instagram. "After 2 years of constant struggle and heartache, 3 miscarriages and a failed embryo transfer…we have a healthy bun in the oven :)) It was a shock to all of us and we found out right before I was going in for my second round of IVF."
The ballroom dancer continued, "I want to thank ALL OF YOU who've been on this fertility journey with me from the beginning. It feels like I'm sharing this news with my extended family. Thank you for sharing your stories and tips to get me through my IVF cycle and thank you for the plethora of encouraging comments and DMs …I read them all. This news has brought extraordinary bliss to our family and we have so much to be grateful for."
As for how Shai learned he was going to become a big brother, the youngster actually figured it out on his own. "We actually told [Shai] in our bathroom," Murgatroyd told ET. "He was looking at my stomach. He's like, 'Mommy, you've got a baby in there'... I was like, 'We do actually'... He was so excited and just jumping around."
ET recently spoke to Chmerkovskiy about expecting baby No. 2. Interestingly enough, the age gap between his two sons is six years -- the same age gap between him and his brother, fellow DWTS star Val Chmerkovskiy.
"I think as long as [Peta and I are] man and man it's good, then after that zone defense is way less complicated, you know, three to two is gonna be tough but we're ready for two, you know, one and one, but again six years difference, he told ET. "I remember experiencing it where [Val] was also my responsibility sometimes, you know, and people do say you don't raise two kids when there's a difference like, that you kind of start passing on and I'm excited to see my son become what my life has always been [a big brother] ... Exactly six years apart, they'll be the same."