The loved-up couple – who tied the knot in 2024 – wrote on Instagram: “This summer we welcomed our sweet baby girl through adoption.”
“We are beyond excited to embark on this beautiful next chapter of parenthood in both peace and privacy [tree emoji].
“And then there were 3.
“Love, Millie and Jake Bongiovi.”
Brown previously admitted that she was looking forward to the challenges of parenthood.
The Stranger Things star – who began dating Bongiovi in 2021 and got engaged to him in 2023 – has always dreamed of starting a family.
During an appearance on the Smartless podcast, Brown said: “My mum actually had her first child at 21 and my dad was 19. And you know, it’s been my thing since before I met Jake. Since I was a baby, I told my mum, like, baby dolls. I wanted to be a mum just like the way my mum was to me.
“And my Nan, my grandmother, is - she was a huge part of my life. And so, yeah, I mean, Jake knows how important it is to me and, of course, I want to focus on really establishing myself as an actor and as a producer, but I also find it’s so important to start a family for me personally.”