Sarah Michelle Gellar has joined the cast of 'Dexter: Original Sin'.

The 47-year-old actress is set to star alongside Patrick Gibson and Christian Slater in the Paramount TV show.

Nina L. Diaz, the president of content and chief content officer of Showtime, said in a statement: "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.

"We’re thrilled to have her return to the SHOWTIME/MTV Entertainment Studios family and join the origin story of the 'Dexter' franchise."

Sarah has also taken to social media to announce the news to her fans.

The actress - whose post featured a photo of the show's script - wrote on Instagram: "It’s going to be a bloody good ride [blood emojis] @sho_dexter (sic)"

Sarah is best known for playing Buffy Summers in the TV drama series 'Buffy the Vampire Slayer'.

And the Hollywood star previously revealed that she regrets not keeping hold of her 'Buffy' outfits.

She told Us Weekly: "I have a couple of pieces, but we weren’t allowed to keep the wardrobe in those days."

Sarah's 14-year-old daughter Charlotte has recently started to embrace some 'Buffy'-inspired fashion trends.

The actress said: "Isn’t that crazy? When my daughter came back and she’s like, ‘Do you still have any chokers?’ I was like, ‘What?’ Or she’ll come out with the white T-shirt with the dress over it."

Despite this, Sarah has never been someone who keeps hold of her old clothes.

The actress - who also has Rocky, 11, with husband Freddie Prinze Jr - said: "I think growing up in New York City, I grew up in a small apartment, and so we didn’t have room. There was never storage. I never grew up with the idea of holding onto this stuff."