“He asked me to be his wife!” the Younger actress, 31, captioned a series of photos with the musician, also 31.
The pics show Duff showing off what appears to be a gorgeous square-cut engagement ring and sharing a smooch with her husband-to-be.
Koma also shared the happy news on Instagram, posting the same shots and writing, “I asked my best friend to marry me... @hilaryduff.”
The announcement has been a long time coming for the pair, who welcomed their first child together, daughter Banks, in October 2018. (Duff also shares son Luca, seven, with ex-husband Mike Comrie.)
A source told E! News at the time that the couple was in no rush to walk down the aisle, however: “They already feel married and don't feel they need a signed document to seal the deal," the source said, noting, "they eventually do want to get married and have a ceremony but for now, are focused on their baby girl coming."
Duff and Koma were rumored to be dating in 2015, though they wouldn’t make their red carpet debut as a couple until January 2017. They briefly called it quits in March, but rekindled their love once more seven months later, and the rest, as they say is history.
"It's going so great," Hilary said on the The Talk in December 2017. "I mean, this is, like, the third time that we've dated...Timing is such a big deal...third time's a charm!"
She continued: "I think that you have history and a past with someone and love, and just because it doesn't work out the first time, the second time, like, as long as there's not too much damage done, then, like, it can always work out again."
As it turns out, she was right: It seems these two are finally ready to tie the knot.
Congratulations, you crazy love birds!