Blake Lively mourns 'Gossip Girl' co-star Michelle Trachtenberg: 'She was electricity'

Blake Lively is remembering the "fiercely loyal" Michelle Trachtenberg.

Lively, who co-starred with Trachtenberg on "Gossip Girl", paid tribute to the actress in an emotional post on her Instagram Story Wednesday. Trachtenberg died Wednesday morning in New York City. She was 39.

"This was the first day I met Michelle," wrote Lively alongside a throwback photo of the two. "She was electricity. You knew when she entered a room because the vibration changed. Everything she did, she did 200%."

Trachtenberg played fan-favorite villain Georgina Sparks opposite Lively's Serena van der Woodsen from 2008-2012.

"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," Lively continued. "She was fiercely loyal to her friends and brave for those she loved, she was big and bold and distinctly herself."

Lively also fondly remembered Trachtenberg's trademark caramel-scented lip gloss, which she said the actress always wore because "she liked creating a nice experience for anyone who was in her orbit, even down to the subtle smell of her lip gloss because she cared about the sweet details."

Trachtenberg was found dead Wednesday at 8 a.m., a spokesperson for the New York Police Department confirmed to USA TODAY. Upon arriving at a luxury apartment building, officers found her unconscious and unresponsive. A cause of death has not been disclosed.

Lively remembered Trachtenberg as a "kind person, through and through."

"The world lost a deeply sensitive and good person in Michelle," she wrote. "May her work and her huge heart be remembered by those who were lucky enough to experience her fire."

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'Gossip Girl' creators, actor pay tribute to Michelle Trachtenberg

Trachtenberg's "Gossip Girl" co-star Ed Westwick, who played Chuck Bass, mourned his former co-star by sharing a photo of her on his Instagram Story.

"So sad to hear of the passing of @michelletrachtenberg sending prayers ??????," Westwick wrote.

Michelle Trachtenberg tributes: Kim Cattrall, Kenan Thompson, more stars mourn actress

"Gossip Girl" creators Josh Schwartz and Stephanie Savage also paid tribute. In a joint statement to USA TODAY, the pair said they are "deeply saddened by the news of Michelle's passing," adding the actress was "so funny, kind and talented."

"Her portrayal of Georgina Sparks was an iconic fan favorite and grew from a one season villain to a beloved character who returned over the course of six seasons," Schwartz and Savage continued. "She was a delight to have on set and will be deeply missed. Our thoughts are with her family."

Contributing: Jay Stahl, USA TODAY

This article originally appeared on USA TODAY: Blake Lively mourns 'Gossip Girl' co-star Michelle Trachtenberg