Production sources tell TMZ ... Paris and Nicole are both on board for a new series that they'll both star in, but we're told this ain't gonna be an exact duplicate of "The Simple Life," per se -- their famous show from back in the day that pretty much put them on the map.

Instead ... our sources tell us this is going to be something with a brand new name -- and while we don't have a sense of the premise just yet ... you can bet it'll be hilarious.

We're being told the project has been talked about among themselves for months -- with Paris and Nicole kicking around ideas on how to do something together again on the small screen. Now, it sounds like they've got their big idea, and they've already sold it to a streamer.

Our sources say it's still very early in development -- and that nothing's been shot yet -- but we know PH and NR are both set to star and be the face of whatever this is.

We're also told there was LOTS of interest from production companies/distributors -- and our sources say an all-out bidding war ensued. We don't where exactly it landed, but our sources do say that James Corden's production company, Fulwell 73, nabbed the rights to shoot it.

Even though this might not be a pure continuation of 'Simple Life' -- ya gotta imagine fans of the original show are rejoicing ... as 'TSL' is still one of the most beloved reality series of all time.

Funny enough, you could argue their fan base might've seen this news coming ... as both PN and NR seemingly telegraphed Wednesday something was in the works, as they both posted the same collage full of throwback photos of themselves.

They were definitely leaning into nostalgia with their respective posts ... and they got their followers buzzing with excitement. Now, those same people are probably over the moon.