Despite their breakup nearly 30 years ago, Richards and Brinson remained close friends up until Brinson's death. Richards reportedly spent a lot of time with Brinson in his final weeks, and gathered with his family around his hospital bed at an assisted living facility.
Richards revealed what her last words to Brinson were as she held him in her arms during his final moments.
"I said, 'I love you,' and then I felt him just kind of leave, and it was shocking," Richards said. "I just didn't expect it."
The estranged couple was married for three years, from 1985 to 1988, and welcomed a daughter, Brooke, in 1986. Brinson died on Jan. 24 after a long battle with lung cancer. He was 58.
His death came after Richards' public struggle with alcohol abuse. In 2015, the 51-year-old reality star entered rehab for the fourth time after she was arrested at the Beverly Hills Hotel for public intoxication in April of last year. Four months later, she was arrested for shoplifting at a Target in Van Nuys, California.
Shortly after the shoplifting incident, a source told ET that Richards had spent months battling alcohol and substance abuse issues and was "getting the help and support she needs."
Richards' appearance on the show will bring to light her troubled relationship with her 21-year-old daughter, Kimberly Jackson, but the former child actress' biggest nemesis on the program seems to be Heidi Montag.
"She likes to stir the [pot]," Richards said of the erstwhile star of The Hills.
The Mother/Daughter Experiment: Celebrity Edition premieres Tuesday at 10 p.m. ET/PT on Lifetime.