On Feb. 21, the pregnant Dancing With the Stars pro shared on Instagram sweet photos of their first meeting with baby nephew Rome Valentin Chmerkovskiy, whom Maks' brother Val Chmerkovskiy welcomed with wife Jenna Johnson in January.
Peta—who is expecting her second child with Maks—included a pic of herself, her husband and their son Shai Aleksander Chmerkovskiy, 6, cradling the fellow DWTS couple's newborn.
"Meeting Baby Rome," she captioned her post. "One of the most special nights for our families. New life, new purpose and new joy!"
The 36-year-old added, "It's been so sweet seeing the both of you @jennajohnson @valentin parent this little angel. We love you all so much XO."
Jenna commented on the sweet post, "Rome loves you so much."
She also reposted a pic of Peta, her son and Rome on her Instagram Stories, writing, "We all cried this night. So much love for this family of mine."
Jenna, 28, also shared more family photos with her son, including a photo of Shai sitting on a couch holding the infant, with Maks and Val standing behind them.
Jenna also included in her post a video of Maks swaying while holding Rome, writing, "Uncle @maksimc first lesson on cucarachas."
The 43-year-old reposted the clip on his Instagram Stories. "Uncleing is awesome!!!" he wrote. "A completely different feeling I've never felt before! Baby Rome is definitely a homie! What a time to be a Chmerkovskiy!"
Last month, Peta revealed how Shai is taking to being a big cousin. I'm astonished at how gentle he is with babies," she told E! News. "He held Jenna and Val's baby the other day and he loved it. He loved holding the paci in his mouth and he was just so good."
Jenna gave birth to Rome—her and Val's first child, Jan. 10 following two years of battling infertility. Meanwhile, Meanwhile, Peta went on her own fertility journey, suffering three miscarriages in the past two years, and began undergoing IVF treatments before falling pregnant naturally. She is due to give birth in June.
"I will never relax until I hear that heartbeat. I just can't," Peta recalled to E! News in January. "I stare at the screen waiting for it to come up. I guess that's what it is this pregnancy. And I'm cool with it."