Some of Smirnoff's former Dancing With the Stars co-stars were a few of the first to comment on the post, including Gleb Savchenko, Tony Dovolani and Lindsay Arnold, who wrote, "Congrats beautiful mama!!!!!! So happy for you!! ❤️❤️❤️❤️."
A source told ET on Wednesday that Smirnoff is "safe, healthy and completely in love with her baby boy."
Due to the coronavirus pandemic, it's obviously been a scary time to welcome a child to the world, but the source said Smirnoff is blessed that everything went smoothly with the birth of her son.
"She feels incredibly blessed," the source said, adding that she is quarantining at home now and enjoying this time with her son. "She is so happy to be a mother."
ET reported earlier this month that Smirnoff had welcomed her first child in Los Angeles the week of April 1. The 42-year-old dancer revealed via Instagram back in December that she was expecting.
"I will have a little one to train on the dance floor!" she captioned a photo of herself holding up a positive pregnancy test at the time. "#BabySmirnoff coming in 2020!"
In more Dancing With the Stars baby news, Artem Chigvintsev is also getting ready to be a first-time dad with his fiancee (and season 25 partner) Nikki Bella.
ET spoke with Nikki this month about what it's like being pregnant during the coronavirus pandemic. She said she's been quarantining with her twin sister, Brie Bella, who is also expecting.
"We're just trying to stay super positive. This is a scary time for everyone, so we're just trying to keep our heads up high, especially for our babies," the Total Bellas star shared. "We're lucky because Artem's here too with us. He's been cooking a lot of our meals. Because we have each other, it's been easy to isolate. We isolated, I want to say, a week before they were really encouraging people to stay home because being pregnant, we are at a high risk, having lower immune systems."
Nikki joked that while she could have never imagined this would be the way her first pregnancy would go, she's fully embracing it and trying to make the best of the situation.
"We've increased our meditation so much, because you try not to panic being pregnant," she said. "I'm already more than halfway through, which I can't believe."