Los Angeles, California - Blake Lively has penned a touching tribute to her Gossip Girl co-star Michelle Trachtenberg after the actor's sudden passing.

On Wednesday evening, the A Simple Favor star honored Trachtenberg on her Instagram Stories with an image of the two on the set of the CW drama as their respective characters, Serena van der Woodsen and Georgina Sparks.

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

The mom of two shared that the late star "laughed the fullest at someone's joke" and "was proud to be a part of this community and industry as painful as it could be sometimes."

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

The Sisterhood of the Traveling Pants alum recounted Trachtenberg would wear "yummy caramel smelling lip gloss" while filming, explaining that Harriet the Spy star "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."

Calling Trachtenberg a "kind person, through and through," she concluded, "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."

Trachtenberg was found "unconscious and unresponsive" in a New York City apartment on Tuesday by her mother and was later pronounced dead by EMS workers at the age of 39.