Article continues below advertisementKelley Mack, known for her roles in 9-1-1 and The Walking Dead, has tragically passed away at the age of 33.Her sister, Kathryn, broke the heartbreaking news through Kelley's Instagram account on Tuesday, August 5. "It is with indelible sadness that we are announcing the passing of our dear Kelley," she wrote. "Such a bright, fervent light has transitioned to the beyond, where we all eventually must go."Article continues below advertisementSource: @itskelleymack/InstagramThe 'Walking Dead' star's sister called her 'a bright, fervent light.