Alyson Hannigan has publicly mourned the passing of her 'Buffy the Vampire Slayer' co-star, Anthony Head.

The actress, known for her role as Willow Rosenberg, shared an emotional tribute on Instagram following the news of Head's death.

Anthony Head, who portrayed Rupert Giles in the popular series, passed away at the age of 72.

His daughters confirmed to BBC News on June 5 that he died from "complications due to pneumonia" and was "surrounded by his family." This news has deeply affected the 'Buffy' community, as evidenced by the outpouring of grief from cast members and fans alike.

Hannigan's Instagram post featured an old photo of herself and Head, accompanied by a heartfelt message.

"This cut is so deep I fear it can never heal.

Oh Tonal…I am so grateful to have had you in my life!

I want to say a million wonderful things about you and yet I can’t seem to find the words that would do you justice," she wrote.

She concluded her tribute with, "I love you so much and will miss you forever.

RIP."

Fellow 'Buffy' star Sarah Michelle Gellar, who played the titular character, commented on Hannigan's post, stating, "He loved you so dearly, Aly." The comments section was filled with condolences from fans, with some noting the recent losses within the 'Buffyverse,' referencing the deaths of Nicholas Brendon and Michelle Trachtenberg.

The shared grief among the cast and fans highlights the lasting impact of the show and its actors.

'Buffy the Vampire Slayer' aired for seven seasons from 1997 to 2003, becoming a significant cultural phenomenon.

The series, which also spawned the spin-off 'Angel', featured a beloved ensemble cast including James Marsters, Emma Caulfield Ford, David Boreanaz, and Seth Green, among others.

The show remains available for streaming on Hulu and Disney+.