Sarah Michelle Gellar knows a thing or two about serial killers.

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The Buffy the Vampire Slayer and I Know What You Did Last Summer alum was cast in the Dexter prequel series, Entertainment Weekly has learned. Gellar joins Dexter: Original Sin in a special guest star role as Tanya Martin, the CSI Chief at the Miami Metro Police Department — a.k.a. Dexter Morgan's new boss.

"Sarah Michelle Gellar is a pop culture icon who perfectly rounds out our best-in-class cast featuring Christian Slater and Patrick Dempsey among others," said Nina L. Diaz, President of Content and Chief Creative Officer for Showtime/MTV Entertainment Studios & Paramount Media Networks. "We’re thrilled to have her return to the Showtime/MTV Entertainment Studios family and join the origin story of the Dexter franchise."

A source tells EW that since the series is set in the '90s, Paramount Global exec Chris McCarthy wanted to capture that time period by casting iconic stars who appeared in seminal TV shows and movies in that era and continue to be stars today, including Slater, Dempsey and now Gellar.

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Set in 1991 Miami, 15 years before the original show, Dexter: Original Sin follows the titular Dexter (originally played by Michael C. Hall, but portrayed here by Shadow and Bone's Patrick Gibson) before he became the prolific serial killer. When Dexter's bloodthirsty urges can’t be ignored any longer, his father Harry (Slater, taking over for James Remar) helps him adopt the Code designed to help him find and kill people who deserve it, keeping his younger sister (originally portrayed by Jennifer Carpenter, but now played Molly Brown) in the dark. But evading the attention of law enforcement proves to be a challenge as he also begins a forensics internship at the Miami Metro Police Department, led by Captain Aaron Spencer (Dempsey).

Dexter: Original Sin is currently in production, with Dexter showrunner and executive producer Clyde Phillips returning at the helm.

Dexter originally ran for eight seasons, from 2006 to 2013, on Showtime, winning four Emmys along the way. Hall reprised his titular role in 10 episodes of a sequel series, Dexter: New Blood, which aired 2021-2022 and was the most-watched series in Showtime history.