Robert Iselin Jr., of Jacksonville, Florida, was shot once in the chest at about 9am on Saturday during a hunting trip in Greenwood County, South Carolina (video below).
Police said Iselin was with a group of hunters that had separated after going into a wooded area.
After being dropped off in a four-wheeler by Iselin, Lucas Brickweg climbed into a hunting stand, according to Fox Carolina.
A short time later, Brickweg heard some rustling nearby. Thinking he had a wild boar in his crosshairs, Brickweg fired a single shot.
When he went to inspect the animal, Brickweg was stunned to find that he had shot and killed Iselin.
"[Brickweg] heard something or saw something and fired. He waited and didn't see anyone or didn't hear anything else. About 10 minutes later, he got down and went over and found his buddy was lying there," said Department of Natural Resources spokesman Capt. Robert McCullough.
Source: Fox Carolina