United Kingdom, June 6 -- Sarah Michelle Gellar is "not OK" following the death of Anthony Head.

The 49-year-old actress has paid a touching tribute to her late Buffy the Vampire Slayer co-star - who played her titular character's mentor and father figure Rupert Giles - after his daughters Emily and Daisy Head confirmed on Friday (05.06.26) he had passed away from complications of pneumonia.

Alongside a number of throwback photos, Sarah wrote on Instagram: " 'Tell Giles I figured it out and I'm ok.' Well I don't have it figured out and I'm not ok.

"But I know I'm the lucky one because I knew you. Thank you to Daisy and Emily who not only shared their dad with me, but with the world."

A host of other Buffy stars have also paid tribute ...