Nate Dogg's Son -- Gold Digging Widow Pounced When Dad Was Mentally Impaired

Nate Dogg's widow doesn't deserve a single red cent of his estate -- according to the hip-hop legend's son ... who claims the marriage was a sham and Latoya Calvin is just trying to cash in now.

According to court docs ... Naijiel Hale says Latoya caused the car accident that led to Nate Dogg having multiple strokes and eventually dying. He also believes she married his father while Nate was mentally incapacitated, so she shouldn't be entitled to anything.

Naijiel's mother, Rhoda Mouton is also joining the fight -- and points out, in docs ... Latoya didn't even attend Nate's funeral.

Nate's estate says he and Latoya separated and filed for divorce 19 days after they married. The only hiccup -- the divorce wasn't final when Nate died.

As we previously reported ... the Dogg's $350k house in Pomona, CA has been the subject of a bitter family feud for years between Latoya and Nate's family -- including his six kids.