Noah Schnapp is godfather to Millie Bobby Brown's daughter

Millie told Entertainment Tonight: "Sadie [Sink] is very, very maternal, but Noah's her godfather."

The actress loves seeing her co-stars interact with her little girl.

She said: "They all turn into the most gooey, soft versions of themselves. Their baby voice comes out when they're around her."

Meanwhile, after being friends since they started work on Stranger Things almost a decade ago, Noah, also 21, admitted it is the "greatest joy" to see the Enola Holmes star at a new stage in her life.

He said: "Aw, it's honestly the greatest joy. It's actually crazy to me to see her grow from such a wide-eyed, innocent, young, silly girl and now she's a mom and married. And I'm just so proud of her."

Millie was just 10 years old when she was cast as Eleven on Stranger Things and she recently expressed her gratitude for the "family" she found on the show.

She told People magazine: "It's taught me a lot of lessons about being a professional person, about being an actor, about being a friend. It's given me the most amazing people in my life to call up when I need them most, and that's my family.

"I'm blessed to have been a part of this show for so many years, and for my childhood to have been recorded. It's a once-in-a-lifetime opportunity."

The Electric State star has vowed not to reveal her daughter's name in public because she and Jake, 23, want to "protect" her from scrutiny.

She told British Vogue magazine: "For me, it's really important to protect her and her story until she's old enough to potentially one day share it herself.

"It's not my place to purposefully put her in the spotlight unwillingly. If she chooses to share her personality one day with the world, like I did when I was young, that's something we'd support. But right now, as she's so little. As he parents, it's our job to protect her from that."

Millie explained that the arrival of the little one has transformed both her and Jake's lives.

She added: "It's been a beautiful, amazing journey - she's taught us so much already. Perspective is a huge thing. The smaller things in life are so much more precious. Our days are filled with lots of cuddles and laughter and love. It's just endless joy."