Wasting no time, the 30-year-old star revealed her bub's gender alongside a couple snap of the parents-to-be.
"Guess what guys! @matthewkoma and I made a little princess of our own and we couldn’t be more excited!!!!!!🤰🏼👶🏼🎀," she captioned the photo.
Koma also shared the happy baby news on his Insatgram, writing an affectionate shout out to his pregnant girlfriend. "She will be as beautiful and sweet as her mother,” he proudly shared.
The former Disney actress and her singer partner have been dating on-again-off-again for years, but in December 2017 she confirmed they were an official couple for the third time.
This will be Koma's first child, while Duff already shares 6-year-old son Luca with ex-husband Mike Comrie.