The late actress's relatively modest Brentwood property -- modest for A-list celebs, that is -- was recently demolished ... and now, photos of the aftermath are surfacing, showing construction crews already hard at work laying the groundwork for something new.

As you can see, her old house -- a roughly 3,000-square-foot structure with 5 bedrooms and 6 bathrooms, complete with a pool -- is practically all gone, meaning the folks moving in did, in fact, want to build out from the ground up without a trace of the former estate intact.

Per real estate records, reviewed by TMZ, the buyers ended up being a dentist and his wife ... and it looks like they filed for a permit to bulldoze back in November. In February of this year, they filed more paperwork signaling they're interested in putting in a new pool and spa.

It would also appear they're geared up to get an entirely new main house built as well. Considering what they've already suggested they'll be putting in -- you can bet it's gonna be a lot bigger than what BW was staying in for quite literally decades.

As many know, Betty had lived at this Brentwood address since the '60s ... and her career in Hollywood got fully in swing shortly after that. Her crib was a staple of celeb sight-seeing for tourists visiting town -- but now, they won't be able to get an eyeful of what was once.

Pretty sad, to be honest. But, when you drop upwards of $10 mil for a piece of real estate -- you're entitled to do whatever the hell you want with it ... regardless of its iconic status.