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,

Blake Lively broke her social media silence on Wednesday to pay tribute to her late “Gossip Girl” co-star Michelle Trachtenberg, who died Wednesday morning at 39. In an Instagram Story, Lively remembered Trachtenberg as a “fiercly loyal” and “kind person, through and through.”