As he took to the stage at the star-studded event in Nashville, Tennessee, Dierks told the audience he was thinking of his pal, and added: "He's going through a tough time right now."
He then launched into an emotional rendition of his tune "I Hold On".
Granger revealed the heartbreaking news of his son's death on social media on Thursday, June 06, writing: "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."
"(Wife) 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."
"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."
Granger and Amber, who are also parents to seven-year-old daughter London, and five-year-old son Lincoln, have been inundated with messages of support from the country music industry following the devastating loss, with stars including Jason Aldean, Maren Morris and Luke Bryan offering their condolences.