One of Floyd Mayweather's ex-girlfriend's children discovered their mum unresponsive in her car and called the emergency services.
Josie Harris was found at around 10pm outside her home in California last Tuesday and attempts to resuscitate her were unsuccessful.
Harris, 40, who had three children with the former fighter, is understood not to have killed herself and no drugs were found at the scene.
Police found no suicide note and her cause of death will now be confirmed by a post-mortem, reports TMZ.
Harris and Mayweather were together for 15 years until 2010 when he assaulted her in front of their children.
Mayweather was later sentenced to 90 days in prison, of which he served two months.
The retired boxer paid tribute to his ex-girlfriend on social media by posting a series of pictures of the pair of them together.
Mayweather called her "My Angel", "my heart", "my love", "my rock", "my family", "my sweetheart" and "my friend" in series of eight pictures.
After his prison sentence, Mayweather rarely saw Harris other than when he picked up his children in person.
In an interview in 2014 Harris said: "(It means) I don't have to take a Xanax before he comes, otherwise I will be sweating bullets.
"For some reason I still get anxiety when I know that he is on his way. I have no idea why, but I get really overwhelmed when I know that I have to be around him."
Of the abuse she suffered at the hands of the former pound-for-pound great, Harris added: "I was a battered woman," she said. "I felt embarrassed about saying I was a battered woman. I felt shame. I felt like it was my fault. What did I do?"
