Michelle Trachtenberg‘s Buffy the Vampire Slayer costars are pouring their hearts out in the wake of her tragic death today.

“I am deeply saddened by the news of Michelle’s passing,” Alyson Hannigan wrote on Instagram. “She brought a loving energy to the set of Buffy. My thoughts are with Michelle’s family and friends.” Hannigan shared the screen with Trachtenberg for three seasons on the supernatural drama as Willow Rosenberg, a trusted friend and confidante to Trachtenberg’s Dawn Summers.

Trachtenberg died on Wednesday at the age of 39. “It is with great sadness to confirm that Michelle Trachtenberg has passed away,” a rep for the actress said in a statement to Entertainment Weekly. “The family requests privacy for their loss. There are no further details at this time.”

Nicholas Brendon, whose character Xander Harris played a major role in Dawn’s life, shared a video of his reaction to Trachtenberg’s death to his Facebook hours after the news broke.

“I didn’t see her much after Buffy, a couple of events together, but when we were working together she was just like a beam of light,” he said, visible with emotion. Dawn, the little sister to series lead Buffy Summers (Sarah Michelle Gellar), always harbored a crush on her sister’s friend Xander, who himself harbored a crush on Buffy. The pair developed a close friendship which eventually evolved into a relationship that turned tragic when Xander stepped up to take care of Dawn through a degenerative spiritual illness.

“I think it was just the last thing I expected, not that I was expecting anyone to die. But I really am sorry to her family,” Brendon continued.

David Boreanaz shared a story to his Instagram that featured a picture of Trachtenberg with the text, “So very sad… horrible news. RIP and prayers to her and her family.”

Boreanaz played Angel, one of Buffy’s primary love interests, for six seasons, sharing two with Trachtenberg. The actress never appeared on Boreanaz’s spinoff series Angel, unlike Gellar, Hannigan, and others, but in later seasons of Buffy her character did admit to harboring a similar childhood crush on Angel as she did on Xander.

Another major Buffy player, James Marsters, shared a touching tribute to Trachtenberg on his Instagram. “My heart is heavy today. We have lost a beautiful soul. Michelle was fiercely intelligent, howlingly funny, and a very talented person. She died much too young, and leaves behind scores of people who knew and loved her,” he wrote.

Marsters played the vampire Spike for six seasons on Buffy, overlapping with Trachtenberg throughout her full tenure. Their characters shared an extremely close bond, with Spike promising Buffy to protect Dawn with his life should anything ever happen to the Slayer. Marsters represented yet another love object for Buffy, and yet another crush for Dawn, but his relationship with Dawn took on a unique, fatherly dimension that won the hearts of fans.

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He continued in his post, “My heart goes out to her family who are good people, and are suffering the greatest loss anyone could bear. I hope everyone can give them space to heal in this most difficult time. Godspeed Michelle. You are missed.”

Emma Caulfield remembered Trachtenberg in a Wednesday Instagram story, writing “I’m so sorry your bright light died so young. Our Buffy family lost a little sister today… Rest in peace lovely Mish Mish. You were loved.”