In February, fans of Buffy The Vampire Slayer and Gossip Girl were shocked to hear that Michelle Trachtenberg had suddenly passed away at age 39. At the time, the CW alum was “believed to have died of natural causes” with no foul play suspected, and ABC News had added that she recently had a liver transplant. Deadline is now reporting that although no autopsy took place, an official cause of death has emerged:

“Following a review of laboratory test results, it was determined that Trachtenberg died naturally as a result of complications from diabetes mellitus, the New York City Office of Chief Medical Examiner told Deadline in a statement.”

Trachtenberg began her career in Harriet The Spy, and her co-star, Rosie O’Donnell, previously reacted to her death with a tribute while adding that Michelle had struggled with health issues over the “the last few years.”

Following that debut, Trachtenberg rose to fame not only with Buffy and Gossip Girl but also a guest appearance on the HBO reboot. Despite her many roles (including EuroTrip and Weeds), most TV viewers remembered her best as Dawn Summers, sister to Sarah Michelle Gellar’s vamp hunter. A Buffy reboot, in which Gellar will make recurring appearances, is in the works, although it’s not known whether Trachtenberg was planning to reprise her role as well prior to her death.