Trachtenberg starred as the cunning Georgina Sparks on the beloved CW series, appearing in each of the six seasons and reprising her role in the recent reboot.

Georgina was played by the actress Michelle Trachtenberg, who was found dead at 39 in her Manhattan apartment on Wednesday. Her performance as the teenage supervillain brought an arch flair to a character who was only a minor figure in the novels that were the basis for the show, but became a fan favorite onscreen.

Lively shared a photo of the day she met Trachtenberg, writing, "The world lost a deeply sensitive and good person"