(CNN) Country singer and songwriter Granger Smith's 3-year-old son has died following a tragic accident.

Both Smith and his wife, Amber Smith, shared the devastating news on social media Thursday that "despite doctor's best efforts, he was unable to be revived."

Smith posted a brokenhearted message to Instagram, calling the news "unthinkable."

"I have to deliver unthinkable news. We've lost our youngest son, River Kelly Smith. Following a tragic accident, and despite doctor's best efforts, he was unable to be revived. Amber and I made the decision to say our last goodbyes and donate his organs so that other children will be given a second chance at life," the singer wrote. "Our family is devastated and heartbroken, but we take solace in knowing he is with his Heavenly Father. Riv was special. Everyone that met him knew that immediately. The joy he brought to our lives cannot be expressed and his light will be forever in our hearts. If there are words to say more, I cannot find them in this moment. Love the ones close to you. There has never been a more difficult moment for us than this."

Amber Smith also shared the news, writing on Instagram that "nothing can prepare a mother to deliver this kind of news."