Actor Michelle Trachtenberg, best known for Buffy the Vampire Slayer and Gossip Girl, died at 39 due to complications from diabetes, ABC News and People magazine confirmed. Her family initially declined an autopsy on medical grounds, but lab testing later revealed the cause.

Her death came as a shock to fans and colleagues alike. A statement released to The Hollywood Reporter read: “It is with great sadness to confirm that Michelle Trachtenberg has passed away. The family requests privacy for their loss.”

Tributes poured in, including one from Gossip Girl co-star Blake Lively, who wrote on Instagram: “Everything she did, she did 200 percent… she was fiercely loyal to her friends and brave for those she loved… Time passes. You take for granted that you get the chance to see an old friend.”

Lively added: “The world lost a deeply sensitive and good person in Michelle. May her work and her huge heart be remembered by those who were lucky enough to experience her fire.”