It’s been nearly 5 months since “The Real Housewives of Orange County” star Lauri Peterson announced the passing of her son, Josh Waring … and TMZ has learned what caused his death.

California’s Orange County Sheriff-Coroner Department tells TMZ … the Bravo personality’s late son died from the combined effects of fentanyl, methamphetamine and olanzapine — with the death officially ruled “accidental.”

Lauri hinted drugs may have played a factor in Josh’s death when she disclosed his passing on Instagram back in April.

As TMZ previously reported … LP shared with her followers that her son died on Easter Sunday, after fighting his addiction struggles “every single day for most of his adult life.”

She continued … “Even during adult hardship, Josh continued to maintain his sense of humor, continued to be optimistic, continued to be kind to others, defended those that were unable to defend themselves and continued to love his family so so much!”

Lauri was an original cast member of ‘RHOC,’ appearing on seasons 1 through 4 before departing the reality show following Josh’s 2008 arrest for heroin possession.

Josh is survived by his daughter, Kennedy, who Lauri adopted back in 2015.

On Mother’s Day, Lauri reflected on Josh’s hardships on Instagram, telling her followers she wished things had been easier for her son.

She added … “I am feeling all the feelings you are experiencing. I’m learning that grief never leaves yet you must learn how to live around that gaping hole in your heart.”

Josh was only 35 years old.