Duff, 29, announced the engagement Thursday on her food blog, The Real Girl's Kitchen. Though fiancé Matt Rosenberg popped the question on Tuesday, his proposal was no joke.
"Matt just took me by total surprise and proposed ... on April Fool's Day of all days! The moment was genuine and sweet (like him!) and I couldn't wait to say yes!" she wrote. "We are so excited and happy to share our wonderful news with everyone!"
Rosenberg, an entrepreneur who owns apparel line Subway Tile Shirts, and Duff have been together a year and a half, her rep tells PEOPLE.
Duff also posted an Instagram photo featuring her hugging Rosenberg – and showing off her gorgeous ring.
The happy news comes after Haylie revealed she's taking her lifestyle brand to TV, premiering her show (also titled "Real Girl's Kitchen") on the Cooking Channel this June.
And the bride-to-be has little sis Hilary Duff's blessing. "So happy to not have to keep this news in!! My beautiful sister and her amazing boyfriend are engaged!!!" the singer Tweeted. Haylie added that she and her betrothed "feel so blessed to have the love and support of our family and friends and can't wait to start this new adventure!"
Reporting by CATHERINE KAST