The actress broke it all down on the latest episode of her podcast -- saying that in June 2023 ... she and Dean were on their way home from a shoot she'd been doing earlier with Jennie Garth, and apparently -- DMD said something to her that crossed the line.

Tori doesn't explain what exactly that was, but she does describe the aftermath, including her throwing a potato on the ground and letting out a guttural scream she calls beast-like.

After that, TS says she locked herself in her bedroom -- one that she says was separate from Dean's own room in the house -- and eventually ... Dean made his way in through a side entrance and told her he wanted a divorce ... which Tori says she was down with.

Obviously, it took a while for her to finally pull the trigger ... but as we all know now, Tori ended up filing for divorce just recently -- this after nearly a year of them being separated.

Tori says once Dean announced their big split on social media, she felt a lot of relief -- noting she felt she could finally move on and that a major weight had been lifted off her chest. However, she does say it was hard for their daughter Stella ... who's a teenager.

As we reported ... Dean recently said the divorce was a long time coming, something he apparently told his kids when they first decided to separate.