Another member of Alana "Honey Boo Boo" Thompson's family is in bad shape -- her Uncle Billy got in a nasty car wreck and suffered major injuries ... and the other driver died.
Sources close to Alana tell TMZ ... Billy -- the younger brother of her father, Sugar Bear -- was involved in a 2-car accident outside Atlanta on Father's Day. We're told he was struck head-on by a driver traveling on the wrong side of the road, and that person was killed.
Sadly, we're told the tragedy has stoked animosity among Honey Boo Boo's family members ... especially toward Sugar Bear. Our sources say they feel like he's abandoning his brother, because he's been practically invisible at the hospital other than visiting Billy once the first week he was there.
Meanwhile, we're told Alana's other uncle, Poodle, has been by Uncle Billy's side almost 24/7.