ATLANTA – An investigation has been launched following a horrific jet ski accident that has left Usher’s 11-year-old stepson brain dead.

Kyle Glover, son of the singer’s estranged wife Tameka Foster, has not experienced any brain activity since he was admitted to a hospital on Friday. Witnesses say the pre-teen and his friend were hit by a jet ski while they were on an inner tube being pulled by a pontoon boat on Lake Lanier in Georgia.

Both children were airlifted to Children’s Healthcare at Egelston Hospital in Atlanta after the accident. The 15-year-old girl suffered a broken arm and lacerations on her head.

According to Georgia Department of Natural Resources rangers, the driver of the Jet Ski was at the lake with a large group of family and friends, including the two children.  DNR officials say the group rented two jet skis and a pontoon boat for the day.

CBS Atlanta reports Monday the driver of the jet ski is 38-year-old Jeffrey Hubbard.

So far, officials have ruled out alcohol as a factor in the accident. They say the driver of the jet ski has been interviewed and they remain in contact with him, but he has not been charged.  After the investigation is completed, DNR officials will turn their recommendation over to the district attorney, who will then decide whether or not charges will be filed.

The DNR’s Critical Incident Response Team is expected to recreate the accident on Monday, as they try to establish exactly what happened.  They will use special computer programs to try to determine how fast both the boat and the Jet Ski were going at the time of the crash.

TMZ.com reports the R&B singer chartered a private jet for his ex-wife, who was out of town when the accident happened, so she could be at her son’s side.  The website said Usher also arrived at the hospital over the weekend.

Many of Usher and Foster’s celebrity friends, including Russell Simmons and singer Fantasia, have taken to Twitter to express their sympathies.

The incident comes just days after the funeral for two brothers killed in a June 18 boat wreck at the lake. Jake and Griffin Prince died when the pontoon boat they were on with family members was struck by a fishing boat.

Follow Kunbi Tinuoye on Twitter at @Kunbiti