Sources told the website she had called off their relationship within the last week.
A police source told and AP that paramedics had to break down the 36-year-old front door before they found him, shirtless and wearing sweatpants, in his bed around p.m.
A friend had called police to say he was unable to get into the home in the So Ho neighborhood of New York.
The details surrounding the death are still unclear, but sources say investigators are looking into the possibility of a drug overdose.
DJ AM was best known for performing at some of Hollywood's most exclusive parties and was previously engaged to Nicole Richie and also dated singer Mandy Moore.