The 29-year-old actress and food blogger shared her big news via Twitter on Thursday night (3 April), while thrilled sister Hilary posted a gorgeous picture of the happy couple – and Haylie's ring!
Hilary tweeted: "So happy to not have to keep this news in!! My beautiful sister @HaylieDuff and her amazing boyfriend @Matt_STS are engaged!!!!"
Haylie told fans her beau had popped the question on April Fools Day and she'd been completely surprised.
"The moment was genuine and sweet (like him!) and I couldn't wait to say yes!" she gushed.
"We are so excited and happy to share our wonderful news with everyone! We both feel so blessed to have the love and support of our family and friends and can't wait to start this new adventure!
Haylie signed off by calling herself The Future Mrs Rosenberg.
Haylie previously appeared alongside her sister on Lizzie McGuire and in the movie Material Girls. She's also appeared in the Broadway production Hairspray and hosted reality show Legally Blonde The Musical: The Search For Elle Woods, which aimed to find the perfect girl to star in the musical show. In addition to acting, she's released several songs and written tracks for sister Hilary.
More recently, the blonde has started her own food blog, Real Girl's Kitchen, which has now inspired a book and upcoming TV show.
Congrats to Haylie and Matt!
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