'Simpsons' Writer Stunned Cypress Hill Prediction Coming True

A fan-favorite 'Simpsons' gag from nearly 30 years ago is about to become a real life event -- courtesy of Cypress Hill -- and the writer who came up with the joke tells TMZ, he's freaking out ... in a good way.

The west coast rap legends -- B-Real, Sen Dog and DJ Muggs -- just announced plans to perform with the London Symphony Orchestra ... a concert idea born from the 1996 'Simpsons' episode, “Homerpalooza.”

On the show, Cypress Hill forgets all about the gig, because, well ... the "Insane in the Membrane" crew got high, of course.

Josh Weinstein, the former 'Simpsons' writer and co-showrunner who came up with the joke, tells TMZ ... he's shocked and overjoyed, fully owning that he predicted the future -- something the internet often credits the show with doing, though it's usually just coincidence.

This time it's not, and no one's happier about it than Josh, who added ... “This is insane, and it is the greatest honor."

Cypress Hill actually did their own voices on the episode -- Josh admits it was his favorite hip hop group, and he wanted to meet them, but he was shocked when they agreed to do it.

ICYMI ... the group announced Wednesday, it will play their “Black Sunday” album in its entirety with the symphony at London's iconic Royal Albert Hall -- and yes, they give full credit to "The Simpsons."

Josh says he's kept in touch with Cypress Hill over the years, and always hoped the unlikely collab he cooked up for Homer and co. would happen in real life.