The 23-year-old ex-popstar, better-known as the cute kid brother of Backstreet Boy Nick Carter, checked into rehab to treat "addiction issues", according to E!.
The source says it was Aaron's own decision to enter the clinic, saying it was his way to "finally get help".
"He was struggling recently and needed this," they said.
Big bro Nick has reportedly been visitng Aaron between rehearsals for the upcoming Backstreet Boys/NKOTB tour and has been "very supportive".
Get well soon Aaron!