12:21 PM PT -- The network from his 2-season show tells TMZ, "The DIY Network family is sorry to hear about the passing of Troy Dean Shafer, a dedicated, driven entrepreneur and restoration expert who was admired by everyone who worked on the series."

They conclude, "We continue to extend our deepest condolences to Troy's family and friends during this difficult time."

"Nashville Flipped" star Troy Shafer died unexpectedly at the age of 38 ... according to his brother.

Troy's brother, Tim, tells us the TV star died in his sleep on April 28. We're told the entire family is in shock because Troy didn't have any known medical conditions.

The coroner's office in Erie, PA confirms an autopsy was not performed on Troy's body, but a toxicology report will be finalized in the coming weeks.

Troy was laid to rest last week, at a very small private burial for his family.

Troy rose to fame by saving, restoring and flipping dozens of historic homes in Nashville ... with a film crew from the DIY Network following him around. Troy and his team specialized in customizing historic properties to fit the design of a certain era.

Before he was a reality TV star, Troy moved to Nashville with dreams of pursuing a career in music ... but he eventually realized his construction background and talent for restoring historic homes was his big ticket, so he started his home renovation business, Nashville Flipped.

He grew up in Erie, Penn., and graduated from Penn State University.

Troy was 38.

RIP