The 30-year-old actress gave birth to a baby girl, Banks Violet Bair, on Thursday, Oct. 25. Koma and Duff both announced the happy news on their Instagram accounts on Monday.
"This little bit has fully stolen our hearts!" Duff captioned a pic of the pair holding their new bundle of joy, huge smiles on both of their faces. "She joined our world at home on Thursday afternoon and is absolute magic ✨."
"We welcome a beautiful daughter, little sister, and best friend for life," Koma captioned his pic as a newly-minted proud papa. "Could not possibly be more grateful for our growing family and for the ? who makes it all possible. Cloud ten."
"Guess what guys! @matthewkoma and I made a little princess of our own and we couldn't be more excited!!!!!!" Duff Instagrammed alongside a picture of Koma sweetly kissing her on the cheek.
Koma, a record producer and songwriter, was also over the moon with the news, writing, "We made a baby girl! She will be as beautiful and sweet as her mother... @hilaryduff another incredible chapter begins."
“Can’t help but imagine this little girl is growing and blooming in my belly like these roses that keep popping up at our house,” she Instagrammed. “Pregnancy is filled with so much emotion and some tough long days, but it sure is special.”
“Feeling lots of love today with every movement and kick to the bladder lol,” she continued. “Appreciate that this one picked Matt and I to be her mommy and daddy. We gunna crush it for you baby B. You have the sweetest big brother waiting to meet and love you."
But later that month, she joked during her appearance on the Today show that Luca was still "on the fence" about being a big brother.
"In this late stage, you are tired of running around and stuff, but we are ready," she added. "I'm so excited."