The sister of Isaiah Thomas was killed Saturday morning in a one-car accident outside Seattle.

Chyna J. Thomas was 22 years old.

The car accident occurred around 5 a.m. on southbound Interstate 5 near South 288th Street in Federal Way, according to the Washington State Patrol.

Witnesses reported that the car, a 1998 Toyota Camry, was being driven normally at first.

“All of a sudden it started to drift very casually onto the left shoulder,” State Patrol spokesman Trooper Nick King said.

The car traveled about 50 feet partially off the roadway until it hit a Jersey barrier.

“That vaulted the vehicle head-on into the sign post,” King said.

According to Celtics' reporter Mark Murphy, Thomas didn't find out about his sister's death until after Saturday's practice.