The Step Up star - who has a six-year-old daughter Everly with ex-husband Channing Tatum - announced the birth of her son, who was born on Friday March 6th.
Dewan, 39, revealed he is named Callum Michael Rebel Kazee and shared a picture of herself embracing her newborn baby.
Writing on Instagram she said: “And just like that, our hearts exploded into all of eternity and beyond.
Welcome to the world you little angel!”
Broadway Kazee, 44, who has become a father for the first time shared a picture of him holding his son’s tiny hand.
He wrote: “In an instant our universe burst wide open and nothing would ever be the same. Welcome to earth star child.”
Dewan and Kazee confirmed they were dating in October 2018 and announced they were expecting their first child together in September 2019. The couple announced their engagement in February.
Announcing her pregnancy last year Dewan said: “Becoming a mother is quite simply the absolute best most incredible thing that has ever happened to me @stevekazee you are a gift from above and i couldn’t be more excited to be expanding our family together...!”
Dewan was previously married to 39-year-old Magic Mike star Channing Tatum, until their split in April 2018.
They met on the set of their movie Step Up in 2006, married in 2009 and have a six-year-old daughter Everly. They were together for 12 years.
Tatum has also found love again with 31-year-old British singer Jessie J. They began dating in October 2018. Despite a brief split in Decemeber 2019 Tatum shared a picture of themselves very much back together on Instagram in January.