The 30-year-old actress announced the news on Instagram today, also revealing the sex of their baby.
“Guess what guys! @matthewkoma and I made a little princess of our own and we couldn’t be more excited!!!!!!” the Younger star’s caption read.
Duff and Koma have had an on-and-off again relationship for some years but rekindled their romance last December after breaking up that March.
At the end of last year, Duff shared with the television show The Talk that the two had resumed their relationship.
“It’s going so great,” she said. “[It’s] the third time that we’ve dated. Timing is such a big deal … third time’s a charm!”
As for the vital mother’s approval, Duff needn’t be concerned.
“My mom was at Matt’s birthday and she was like, ‘I just love him. I love him so much. He’s the best,’” she told E! News.
The actress’ pregnancy announcement came just days after sister Haylie Duff gave birth to her and fiancé Matt Rosenberg’s own baby girl, LuLu Gray.
Duff has a six-year-old son Luca Cruz Comrie with her then-husband and ice hockey player Mike Comrie. They were married between 2010 and 2016.