Convicted Double Murderer Betty Broderick Died After Serious Fall, Septic Infections

Betty Broderick -- the woman who fatally shot her ex-husband and his new wife back in 1989 -- died in the ICU Friday following a number of health issues, TMZ has learned.

Betty's son, Daniel Broderick, tells TMZ ... she had a number of septic infections -- including one infection that she had years ago and came back. Plus, she had a serious fall at the Californian Institute for Women where she was locked away about 3 weeks ago ... which resulted in broken ribs.

Daniel says Betty ended up in the ICU at a hospital off the prison grounds. She was on life support at the end of her life and unable to communicate.

Daniel and his 3 siblings were all bedside when she passed Friday morning.

Betty was serving a 32-year-to-life sentence for murdering her ex-husband Dan Broderick and his wife, Linda, when she died.

Dan admitted to having an affair with Linda, his much-younger assistant, while he was married to Betty -- years after she confronted him about her suspicions. Betty was so pissed she ended up stealing her daughter's key to Dan and Linda's home 7 months after they were married and shot them to death in cold blood.