An investigation is now underway into Friday's tragic jet ski accident that left Usher's stepson brain dead.

According to ABC News, Jeffrey S. Hubbard, 38, was operating the jet ski when it collided with Kyle Glover, 11, the son of Usher's ex-wife, Tameka Foster. Hubbard is a family friend of Usher and Foster.

PHOTOS: Celebrity health scares

"The accident is under investigation, and Hubbard is [under investigation] as the operator of the personal watercraft," Sgt. Mike Burgamy with the Georgia Department of Natural Resources said.

Glover was riding an inner tube on Lake Lanier in Atlantic, GA on Friday with an unidentified 15-year-old girl. Both children were airlifted to Children's Healthcare of Atlanta at Egleston after the accident. Glover was hit in the head and registered no brain activity since he was admitted. The second victim reportedly suffered a broken arm and cut on her head.

Burgamy explained, "A pontoon was pulling the two adolescents on an inner tube, and the personal water craft went over the top of them."

PHOTOS: Dads on duty

Usher (real name: Usher Terry Raymond IV), 33, and Foster divorced after two years of marriage in 2009. The couple share sons Usher Raymond V, 4, and Naviyd, 3, in addition to Kyle, Foster's son from a previous relationship.

Despite being engaged in a heated custody battle before the accident, Usher and Foster have put it aside to support each other. "Tameka and Usher don't get along, but in this circumstance Usher is coming to her side," a source told Us Weekly. "Usher practically raised Kyle as his own. He's known him for seven years. It is so sad what happened." 

PHOTOS: Usher and other stars in concert

Another source told Us, "He loved Kyle. This is a terrible, awful tragedy. Usher is torn up."

This article originally appeared on Usher's Family Friend Under Investigation Over Stepson's Jet Ski Accident