Sarah Michelle Gellar Teases Unexpected ‘McBuff’ Crossover with Patrick Dempsey for “Dexter” Prequel

The pair appear as two Miami Metro Police Department officers in the prequel series

Sarah Michelle Gellar and Patrick Dempsey are ready to take on the world of Dexter.

The two actors, who are set to appear in the prequel series Dexter: Original Sin, teased their new TV series in a Monday, Sept. 16 Instagram post Gellar shared. The fun selfie shows Gellar and Dempsey in their costumes.

The Grey’s Anatomy alum, 58, stars in the Paramount+ with Showtime series as Miami Metro Homicide Captain Aaron Spencer. Meanwhile, the Buffy the Vampire Slayer star, 47, has a special guest role as Tanya Martin, the CSI chief at the Miami Metro Police Department and Dexter’s new boss at a forensics internship.

“The crossover you didn’t know you needed (#McBuff?!?),” Gellar captioned the post, referencing their past hit shows.

Gellar played Buffy Summers, a teenage vampire slayer, on Buffy, which ran for seven seasons from 1997 to 2003. Dempsey starred as Dr. Derek "McDreamy" Shepherd in the first 11 seasons of Grey's Anatomy, from 2005 to 2015.

Related: Dexter: Original Sin's Dark Teaser Promises a Look at the Makings of an Iconic Killer

Several fans called out the duo’s appearances in the Scream franchise. “I would say Scream 2 meets Scream 3 ??,” commented one user. Gellar starred as Cici Cooper in Scream 2 (1997), while Dempsey starred as Detective Mark Kincaid in Scream 3 (2000).

Dexter: Original Sin also stars Patrick Gibson as Dexter Morgan and Christian Slater as his father, Harry.

PEOPLE previously reported in June that the casting of Gellar, Slater and Dempsey was a deliberate decision by network executives to help "capture" the 1990s period the show is set in. They chose actors who had appeared in notable projects throughout that decade and who continue to be stars today.

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The upcoming prequel series will follow the iconic character as he “transitions from student to avenging serial killer.”

“When his bloodthirsty urges can’t be ignored any longer, Dexter must learn to channel his inner darkness,” according to the synopsis. “With the guidance of his father, Harry he adopts a Code designed to help him find and kill people who deserve to be eliminated from society without getting on law enforcement’s radar. This is a particular challenge for young Dexter as he begins a forensics internship at the Miami Metro Police Department.”

Dexter: Original Sin follows the eight-season run of Dexter, starring Michael C. Hall and Jennifer Carpenter, from 2006 to 2013 and spawned the miniseries Dexter: New Blood.

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The new series premieres on Paramount+ with Showtime on Friday, Dec. 13.

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