Michelle Trachtenberg, known for her roles in "Gossip Girl" and "Buffy the Vampire Slayer," has died at age 39.

Police sources confirmed the devastating news to The New York Post, and her death is reportedly not being investigated as suspicious. The cause remains unclear.

In recent months, the former child star shared troubling social media posts, appearing gaunt and frail.

She defended her appearance, calling out "haters" and saying, "Explain to me how I look sick." She also reminded followers ... "Did you lose a calendar and not realize I’m not 14. I’m 38. How sad for you to leave such a comment.”

In another post, she made it clear that she never had plastic surgery and was "happy and healthy."

Michelle rose to fame as a child star in "Harriet the Spy" -- later becoming a household name in her role as Dawn Summers on "Buffy the Vampire Slayer," then took on the Upper East Side as Georgina Sparks in "Gossip Girl."

She was 39.

RIP