Michelle Trachtenberg died due to natural causes, as a result of complications from diabetes mellitus. The New York City Office of Chief Medical Examiner confirmed the results to People on Wednesday.

Trachtenberg was discovered unconscious and unresponsive in her Manhattan apartment on the morning of Feb. 26. The “Harriet the Spy” and “Buffy the Vampire Slayer” actor’s family had declined an autopsy at the time after the NYPD determined that there was no evidence of foul play or criminality.

Beginning work as a child actor, Trachtenberg appeared in the ’90s Nickelodeon series “The Adventures of Pete & Pete” before starring in the family film “Harriet the Spy” in 1996 at the age of 10. As a teenager, she featured as Dawn Summers in “Buffy the Vampire Slayer,” joining the series in Season 5 and staying involved until its wrap. She also played the villainous Georgina Sparks on the teen drama “Gossip Girl,” recurring through the show’s run from 2007 to 2012.

“Trachtenberg’s untimely death, at 39, marks a passage for millennials — she was one of the signature young stars with whom this generation grew up,” wrote Variety‘s chief correspondent Daniel D’Addario in a tribute after he death. “On the cult-favorite Nickelodeon show ‘The Adventure of Pete & Pete,’ she provided deadpan ballast to the show’s surrealist trappings. She allowed a way into the proceedings on ‘Buffy the Vampire Slayer’ for young viewers, playing Buffy’s little sister Dawn, one of the show’s emotional fulcrums. Later, on ‘Gossip Girl,’ Trachtenberg’s Georgina Sparks was a gleeful agent of chaos — taking the fast-ticking mind and the acuity with a sharp insult that the actress had exhibited in ‘Harriet the Spy’ and flipping it on its head.”