A grieving father whose son died from a fentanyl overdose has a heartbreaking warning for users of the drug.

"This is how much fentanyl it takes to kill you!" Brett Gibney of Cocoa, Florida, wrote last month in a Facebook post that featured a photo of a small bag of powder.

"BTW ... this is not fentanyl, heroin, or meth," continued the post, which has been shared 23,000 times. "This is my sons ashes!!! Remember this picture next time you want to get high! Share this post ..."

>> See the post here

According to WBNS, Gibney's son, Brent Gibney of Columbus, Ohio, was in jail on robbery charges when he overdosed on fentanyl Oct. 1. He died three days later at age 29. His death is still under investigation, authorities said.

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Gibney hopes his viral post will prevent another family from going through the pain he's experienced.

"If this saves one life from a fentanyl overdose, we've accomplished our mission," he told WBNS.

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