The actress and her husband, Chris Wood, quietly became parents to a son named Huxley Robert Wood over the summer, but only broke the news to fans on Instagram on Friday (25Sep20).
Alongside a snap of the tiny tot's hand, Benoist wrote, "Huxley Robert Wood got here a few weeks ago and this little boy is everything."
Wood, who wed Benoist a year ago, shared the same image on his social media page, gushing about their "amazing" son, and then joking about keeping him off social media for the foreseeable future.
"And no it's probably none of your business... brb (be right back) see you in 18 years," he quipped.
Benoist's new role as a mum comes as she prepares to bid farewell to her time as Supergirl, which TV bosses announced on Tuesday will wrap for good after its upcoming sixth season.
"To say it has been an honor portraying this iconic character would be a massive understatement," she said. "Seeing the incredible impact the show has had on young girls around the world has always left me humbled and speechless."
"She's had that impact on me, too. She's taught me strength I didn't know I had, to find hope in the darkest of places, and that we are stronger when we're united. What she stands for pushes all of us to be better. She has changed my life for the better, and I'm forever grateful. I'm so excited that we get to plan our conclusion to this amazing journey, and I cannot wait for you to see what we have in store."
"I promise we're going to make it one helluva final season (sic)."