Michelle Trachtenberg attends Cadillac Celebrates the 92nd Annual Academy Awards at Chateau Marmont on February 6, 2020 in Los Angeles, California. Photo:

JC Olivera/WireImage

Michelle Trachtenberg’s cause of death has been revealed.

The New York City Office of Chief Medical Examiner confirmed to PEOPLE on Wednesday, April 16, that the actress’ sudden death was a result of complications of diabetes mellitus. The manner of death was ruled as natural.

A spokesperson for the New York City Office of Chief Medical Examiner tells PEOPLE “the amended determination was made following review of toxicology testing results.” According to the spokesperson, “toxicology testing can be done without autopsy.”

This comes less than two months after Trachtenberg was found dead in a New York City apartment when law enforcement responded to a 911 call on Feb. 26. After officers arrived, they found a woman, identified as Trachtenberg, unconscious and unresponsive.

The New York City Medical Examiner’s Office told PEOPLE the next day that the Gossip Girl alum’s family objected to an autopsy, meaning that her cause of death would be ruled “undetermined.”

Following the news of her death, sources told PEOPLE that Trachtenberg had recently undergone a liver transplant and may have experienced complications. A separate source told PEOPLE that Trachtenberg had been “really really down emotionally” and had “told friends she was struggling” in the last year.

Michelle Trachtenberg. John Salangsang/Variety/Penske Media via Getty

“She was really, really sick and open with those in her circle about how much she was struggling,” the insider said. “She was “pale, gaunt, very thin, and dealing with health issues.”

Despite the health concerns, Trachtenberg had spoken out against critics in January 2024 who made comments about her appearance after she shared a selfie on Instagram. “Fun fact. This is my face,” she wrote at the time. “Not malnutrition no problems. Why do you have to hate? Get a calendar.”

The late actress was best known for her roles as Georgina Sparks on Gossip Girl and Dawn Summers on Buffy the Vampire Slayer. Her entertainment career began after she landed roles on Nickelodeon’s The Adventures of Pete & Pete and soap series All My Children.

Michelle Trachtenberg attends Michael Muller’s HEAVEN, presented by The Art of Elysium, on January 5, 2019 in Los Angeles, California. Kevin Winter/Getty

Trachtenberg’s former costars mourned her death on social media after the news broke.

“This was the first day I met Michelle,” Blake Lively wrote in part, alongside a photo of the pair from Gossip Girl. “She was electricity. You knew when she entered a room because the vibration changed. Everything she did, she did 200%.”

Her Buffy costar, Sarah Michelle Gellar, remembered Trachtenberg with a carousel of photos from their time together on the show.

“Michelle, listen to me. Listen. I love you. I will always love you,” Gellar, 47, wrote to Trachtenberg, quoting from the season 5 finale episode of Buffy in which Buffy sacrifices herself for Dawn. “The hardest thing in this world, is to live in it. I will be brave. I will live… for you.” She added “💔💔💔🗝️” to the end of the caption.

Never miss a story — sign up for PEOPLE’s free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human interest stories.

Rosie O’Donnell, who starred with Trachtenberg in Harriet the Spy, shared in an exclusive statement to PEOPLE that hearing what happened was “heartbreaking.”

“I loved her very much. She struggled the last few years. I wish I could have helped,” she added.