'X Factor' Star Simone Battle Found Dead at 25

Singer Simone Battle, who rose to fame on the US version of "X Factor" ... was found dead in her Los Angeles home ... 

25-year-old Battle was a singer in the girl group "GRL" ... which was the reboot of the Pussycat Dolls. She signed on with the group after her run on "X Factor" ... where she was a finalist, making it into the top 17.

The L.A. County Cororner's Office tells us Battle's autopsy has not been completed yet ... so, nothing has been ruled out as cause of death.

We've spoken to Simone's father ... and he says the family is still unaware of how she died. He told us Simone was found in the bedroom of her apartment in a West Hollywood neighborhood. He described her home as a guest house of a larger residence.