Michelle Trachtenberg’s death at just 39 years old has shocked both her fans and former collaborators. But those who encountered her in her final days say the signs were there that something was very wrong.

Blake Lively paid tribute to her Gossip Girl costar Michelle Trachtenberg. Yesterday, news emerged that the actor had died at age 39. Though her cause of death is still unknown, police sources noted that she recently underwent a liver transplant.

Comedian and former Nickelodeon child star Kenan Thompson shared a video on Instagram of the two of them on Nick, writing: “Our first Nick movie star has departed us!! She was my friend and now she rests!!” One of Trachtenberg’s first roles was in the Nick series “The Adventures of Pete & Pete.”