The “Lizzie McGuire” alum shared the happy news on her Instagram on Saturday.
“Mae James Bair – We LOVE you beauty,” she wrote, along with the date March 24 written out in numbers, the day the little one was born.
Duff, 33, shared a black-and-white photo of her now family of five. In the pic, Duff is sitting in an inflatable bath filled with water, holding the newborn in her arms as she’s surrounded by her other daughter, Banks, 2, son Luca, 9, and husband, Matthew Koma.
Several celebrities reacted to the “Younger” star’s post on Saturday.
“So beautiful! Congratulations!! Ashlee Simpson Ross said.
“Congratulations mama!!!” Sophie Turner wrote.
“Omg how amazing this is! Congratulations,” Jenna Dewan commented.
“Married at First Sight” alum Jamie Otis added: “CONGRATS MAMA! Women are so incredibly strong. You literally just grew the cutest tiny human and birthed it! It will never cease to amaze the power of a woman. Enjoy that precious babe!
She first announced her third pregnancy in October, writing on Instagram, “We are growing!!! Mostly me…”
Mae is Duff’s second child with Koma, whom she married in December 2019. She shares her son, Luca, with her ex-husband Mike Comrie.