Duff captioned the photo, in which she wears a maxidress that shows off her baby bump and Koma kisses the side of her head. She will be as lovely and sweet as her mother.
Earlier this week, Duff told HuffPost at a Build event that Koma was even writing new music for her but insisted she has no plans for a new album anytime soon.
The happy family were seen hanging out with some friends before they headed to a sushi dinner together.
This will be Duff's second child, as she shares son Luca with ex-husband Mike Comrie.
Her 31-year-old musician beau looks all ready for fatherhood as he was seen carrying Hilary's eldest child before they hopped in the vehicle together. The baby will also have a playmate in Hilary's new niece Lulu, who was born to her sister Haylie on Thursday. Hilary, 30, confirmed she and Koma were back together in December previous year, after the duo dated for a few months before breaking things off in March.
She warned, "Besides, watch, I'll probably get some evil spawn of Hilary the next time around".
"It's going so great", she said on "The Talk," saying it is "the third time that we've dated". He's the best.' I'm like, 'I'm here.
The star wrote on Instagram, "Guess what guys!" I exist, you know? "My mom was at Matt's birthday and she was like, 'I just love him. You're always on my side!' She's such a traitor!"