Bobbie Jean Carter, Nick & Aaron Carter's Sister, Found Unresponsive in Bathroom

Nick and Aaron Carter's sister, Bobbie Jean Carter, was found unresponsive in a bathroom the day she died ... just like her late brother Aaron.

The Hillsborough County Sheriff's Office tells TMZ ... first responders were dispatched to Bobbie's Tampa, FL home Saturday morning, they found her and rushed her to a nearby hospital, where she was declared dead.

The sheriff says deputies learned Bobbie Jean was on probation for cocaine possession when she died, but her roommates told police she had not used any narcotics since being released from prison.

What's more, we're told deputies did not find any narcotics or drug paraphernalia in Bobbie Jean's bedroom or bathroom ... and there were no signs of foul play.

The sheriff says Bobbie Jean's death is under investigation ... and her official cause of death will be ultimately determined by the Medical Examiner's Office, pending toxicology results.

It's pretty eerie to learn Bobbie was found unresponsive in a bathroom ... because the same thing happened with Aaron.

Remember ... Aaron died last year after drowning in his bathtub. The autopsy report said Aaron became incapacitated due to the effects of prescription pills and huffing before slipping under the water and drowning.