The Gossip Girl family is mourning Michelle Trachtenberg.

Chace Crawford, who played Nate Archibald on the CW show, posted a tribute to the late actress, who was found dead in her apartment Wednesday morning.

“Michelle was one of a kind,” Crawford wrote on Instagram. “I remember her coming on set for the first time and just absolutely owning it. She was a force of nature and just so so unapologetically funny and magnetic.. remembering those years with a big smile. Just a terrible loss. Love you.”

Blake Lively, who played Serena van der Woodsen, enduring frienemy to Trachtenberg’s Georgina Sparks, posted a lengthy and heartfelt remembrance of the late actress on her Instagram.

“This is the first day I met Michelle. She was electricity,” she wrote over a still of the two conversing in character on the popular teen drama. “You knew when she entered a room because the vibration changed. Everything she did, she did 200%. She laughed the fullest at someone’s joke, she 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.”

Ed Westwick, who played the sleazy Chuck Bass on the series, also shared his condolences on Instagram: “So sad to hear of the passing of @michelletrachtenberg. Sending prayers.”

Gossip Girl co-creator Josh Schwartz also wrote a message memorializing Trachtenberg. “RIP Michelle,” he said in an Instagram story. “Thank you for Georgina. You will be missed but not forgotten.”

Grace Duah, who portrayed Shan Barnes in the two-season 2020s Gossip Girl reboot, posted a photo of Trachtenberg in Ice Princess, writing, “xoxo princess.”

Marriage Story actor Azhy Robertson, who played the son of Trachtenberg’s character in one episode of the GG revival, also reacted to the actress’ death. “Sad to hear this news,” he wrote in an Instagram story. “We really lost someone special.”

Trachtenberg played the conniving, recurring guest character in 28 episodes of the original Gossip Girl series, which ran from 2007 to 2012. She appeared in all six seasons of the series, with an expanded role in the final season. Trachtenberg also reprised her role in two episodes of the 2021 GG revival.

Trachtenberg’s cause of death is not yet known. Sources told ABC News that the 39-year-old actress had recently received a liver transplant and “may have been experiencing complications” from the procedure.

Trachtenberg’s Georgina was a forceful presence on Gossip Girl. Though her character typically only showed up for a few episodes in a given season, any time she appeared, audiences knew that the chaos of the show’s interpersonal drama was about to ramp up several notches. 

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Georgina was one of GG‘s most energizing catalysts, brilliantly weaponizing and deepening the rifts between primary characters while also sometimes serving as a common enemy that tenuously united rivals against her. In a show characterized by backstabbing and manipulation, Trachtenberg’s character always went to the next level, deceiving and controlling her peers by drugging, seducing, and misleading them with a duplicitous pregnancy.

Trachtenberg was also known for her work on Buffy the Vampire Slayer, playing Dawn Summers, the younger sister of Sarah Michelle Gellar‘s protagonist. As a child actress, she also appeared in notable projects like Harriet the Spy, Inspector Gadget, and The Adventures of Pete & Pete. As an older teen, she acted in Gregg Araki’s dark indie drama Mysterious Skin, the sex comedy EuroTrip, and the Disney figure skating comedy Ice Princess.

The actress also appeared in films like Black Christmas, 17 Again, Cop Out, and Take Me Home Tonight. On the small screen, she appeared in episodes of Weeds, Love Bites, Criminal Minds, and NCIS: Los Angeles.