Blake Lively and Alyson Hannigan are among the former "Gossip Girl" and "Buffy" actors mourning the death of their one-time co-star, Michelle Trachtenberg.

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,

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.