Sarah Michelle Gellar tells PEOPLE about when Buffy the Vampire Slayer premiered in 1997 and why she didn’t know the show was a hit for quite some time; Gellar immediately start

Sarah Michelle Gellar shared an Instagram video Thursday introducing Ryan Kiera Armstrong, the star of Hulu's "Buffy, the Vampire Slayer" revival. Gellar will co-star and produce.

Ryan Kiera Armstrong has staked the role of the new slayer in town in the upcoming "Buffy the Vampire Slayer" revival. The 15-year-old actor will co-star with original series lead Sarah Michelle Gellar. The two actors shared the news May 15 in a joint Instagram post featuring a video that showed Gellar breaking the casting news to Armstrong.