Usher arrives at the Billboard Music Awards on May 20, 2012 in Las Vegas, Nevada. Credit: Frazer Harrison/Getty

Tragic news for Usher and his family.

The Grammy-winning singer's 11-year-old stepson, Kile Glover, has been declared brain dead after being accidentally struck with a jetski, TMZ reports.

Kile, the son of Usher's ex-wife Tameka Foster, was riding an inner tube on Lake Lanier in Atlanta, GA on Saturday when a jetskier hit him -- striking him in the head and knocking him unconscious.

Kile was airlifted to a nearby hospital, where Usher, 33, is said to have joined him Sunday evening. TMZ reports that Kile has registered no brain activity since being admitted.

Authorities are investigating the accident, although alcohol has already been ruled out as a contributing factor.

Usher (real name: Usher Terry Raymond IV), 33, divorced Tameka in late 2009 after two years of marriage. In addition to Kile, Tameka's child from a previous relationship, the duo share sons Usher Raymond V, 4, and Naviyd, 3. The former spouses have been in a protracted custody dispute.