WASHINGTON (AP) — A driver so enamored of his Tesla Model S sedan that he nicknamed the car "Tessy" and praised the safety benefits of its sophisticated "Autopilot" system has become the first U.S. fatality in a wreck involving a car in self-driving mode.

The National Highway Traffic Safety Administration announced the driver's death Thursday, and says it is investigating the design and performance of the Autopilot system.

Officials say the victim, 40-year-old Joshua D. Brown of Canton, Ohio, was killed May 7 in Williston, Florida, when his car's cameras failed to distinguish the white side of a turning tractor-trailer from a brightly lit sky and didn't automatically activate its brakes.

Just one month earlier, Brown had credited the Autopilot system for preventing a collision on an interstate.