Michelle Trachtenberg was found in her New York City apartment, and the death is not believed to be suspicious, police said.

Michelle Trachtenberg's cause of death was revealed Thursday after the 39-year-old actress was found dead in New York City Wednesday morning.

Trachtenberg starred in 28 episodes of “Gossip Girl” as Georgina Sparks, a recurring character and frenemy of Lively’s Serena van der Woodsen. Georgina, also a member of the Upper East Side’s high society, was notoriously rebellious and known for getting herself and those around her into trouble.

Michelle Trachtenberg's memorable movie and TV roles, including 'Gossip Girl' and 'Buffy' Michelle Trachtenberg, who found fame as a child star, became beloved 'Gossip Girl' actre

Actress Michelle Trachtenberg, known for roles in "Buffy," "Harriet the Spy" and "Gossip Girl" was found dead in New York City Wednesday at age 39.

Trachtenberg starred in a variety of kid-oriented movies and shows, making her film debut in 1996’s “Harriet the Spy.”

Lively was not the only castmember of the beloved teen drama to honor Trachtenberg, who was also known for roles in Buffy the Vampire Slayer and Harriet the Spy. Other Gossip Girl stars including Ed Westwick and Chace Crawford also reacted to her death on social media.

Trachtenberg was 39. Police found her “unconscious and unresponsive” in a Manhattan apartment on Wednesday morning.

Earlier on Wednesday, an NYPD source told CNN that Trachtenberg ... Then came a moment of reinvention, thanks to the CW’s “Gossip Girl,” on which she played the deliciously villainous ...

Police responded to a 911 call early Wednesday morning at a residential tower in midtown New York City where “officers observed a 39-year-old female unconscious and unresponsive,” according to an NYPD statement.

Trachtenberg starred in a number of children's movies before getting a breakout role as Dawn in "Buffy the Vampire Slayer."