Shiloh Jolie-Pitt -- who just turned 18 a few days ago on May 27 -- filed paperwork requesting a legal name change ... specifically, dropping the "Pitt" from her last name and making her new name simply "Shiloh Jolie."

Mind you ... this doc was literally filed on Monday, which was on Memorial Day ... and also happens to be her 18th birthday. So, it seems this was one of the first things she wanted to do as an adult.

Of course, it's incredibly telling ... it's no secret Brad has had a strained relationship with some of his kids since he and Angelina filed for divorce in 2016 -- an ugly split that has dragged on in court, even to this day.

Shiloh's request for the name change has yet to be granted -- but it's only a matter of time before it becomes official. As you know, Shiloh is one of Brad and Angie's three biological children ... they have 3 other adopted children, including 19-year-old Zahara Jolie ... who also doesn't use Pitt in her name these days.

In fact ... their other daughter -- 15-year-old Vivienne -- reportedly has also been avoiding using "Pitt" in naming herself ... she was only listed as Vivienne Jolie on a playbill for an Angelina-produced Broadway musical she was recently working on as PA.

When it comes to Maddox -- who's 22, and the oldest of the bunch -- he reportedly also doesn't use "Pitt" in his surname anymore ... but it appears as if Shiloh is the only one of the kids who's filed to make it count in court.