Posting the news alongside a photo of him with his beloved boy, Smith said his son had died in a 'tragic accident'.
The boy was the youngest child of Smith and his wife Amber who also have son Lincoln Monarch, five, and a and seven-year-old daughter London.
His heartbroken wife Amber also posted about the tragic news on her Instagram account, writing: 'Nothing can prepare a mother to deliver this kind of news. We've lost our youngest son, River Kelly Smith.'
It is not known exactly how River Kelly died but Granger Smith described how he was 'unable to be revived' despite the best efforts of doctors.
Following River Kelly's death they decided to donate his organs to save the lives of others.
The family who live in Georgetown, Texas have asked for donations to Dell Children's Medical Center instead of flowers.