"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!" the 29-year-old actress and blogger wrote.
"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!" she added.
Duff's little sister, Hilary, was quick to offer her support on Twitter.
"So happy to not have to keep this news in!! My beautiful sister @HaylieDuff and her amazing boyfriend @Matt_STS are engaged!!!!" Hilary tweeted.
Hilary separated from husband Mike Comrie earlier this year.
Swim Week Miami Beach 2014 [PHOTOS]