Blake Lively is mourning the loss of her former Gossip Girl costar Michelle Trachtenberg after the actress’ death.

“This is the first day I met Michelle. She was electricity,” the A Simple Favor star, 37, wrote in a tribute on her Instagram Stories alongside a throwback photo of her Gossip Girl character, Serena van der Woodsen, chatting with Michelle’s Georgina Sparks on Wednesday, February 26. “You knew when she entered a room because the vibration changed. Everything she did, she did 200 percent.”

Blake added that Michelle, who died at 39 years old on Wednesday, “laughed the fullest at someone’s joke” and “faced authority head on when she felt something was wrong.”

“She cared deeply about her work, she was proud to be a part of this community and industry as painful as it could be sometimes, she was fiercely loyal to her friends and brave for those she loved, she was big and bold and distinctly herself,” the It Ends With Us actress continued. “And she always had yummy caramel smelling lipgloss on because she didn’t just want to sparkle on camera, she liked creating a nice experience for anyone who was in her orbit, even down to the subtle smell of her lipgloss because she cared about the sweet details.”

Blake also called Michelle a “kind person, through and through” before reflecting on the loss of her former castmate.

“Time passes. You take for granted that you get the chance to see an old friend. To paraphrase, the real tragedies in life are the ones that blindside you on an idle Tuesday,” she wrote.

Blake concluded, “Hold those you love and have loved dear. 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.”

Michelle appeared throughout Gossip Girl’s six-season run between 2007 and 2012 as Georgina Sparks, a longtime frenemy of Serena’s who often wreaked havoc within the Upper East Side’s social scene. Michelle reprised her role in the 2022 reboot.

Michelle was found dead in her New York City apartment, a spokesperson for the Deputy Commissioner of Public Information for the New York Police Department confirmed in a statement to In Touch.

“On Wednesday, February 26, 2025, at approximately 0801 hours, police responded to a 911 call of an aided individual at 1 Columbus Place, within the confines of the Midtown North Precinct. Upon arrival, officers observed a 39-year-old female unconscious and unresponsive. EMS responded to the location and pronounced the victim deceased,” the statement read.

The victim was then identified as Michelle. Her death is not being investigated as suspicious at this time, and an investigation is ongoing, according to the statement.

While Michelle’s cause of death has yet to be confirmed via an autopsy, sources told ABC7 that the Criminal Minds alum recently underwent a liver transplant and may have experienced complications as a result of the surgery. An insider told the New York Post her body possibly rejected the organ.

In addition to Gossip Girl, Michelle was known for her role as Dawn Summers on Buffy the Vampire Slayer from 2000 to 2003. She also starred in the films Harriet the Spy (1996), Inspector Gadget (1999), EuroTrip (2004), Ice Princess (2005) and 17 Again (2009).