Michelle Trachtenberg, who died this February, would have turned 40 on Friday, and her Buffy the Vampire Slayer sister Sarah Michelle Gellar marked the somber occasion on Instagram.
“When you turned 16, it was hard not to still see you as the little girl I met on All My Children,” Gellar wrote, addressing her late costar. “When you turned 21, I had to teach myself to not see you as the little sister anymore. I can’t imagine what 40 would have been like. This I know… it would be filled with love. Happy birthday @michelletrachtenberg.”
In the final three seasons of Buffy, Trachtenberg played Dawn Summers, the younger sister of Gellar’s Buffy Summers. Previously, she played Lily Montgomery on All My Children from 1993 to 1996, overlapping with her future Buffy sis as Gellar filled the role of Kendall Hart on the daytime drama.
Trachtenberg’s other credits included a lead part in the 1996 film Harriet the Spy and a starring role in the original Gossip Girl.
The actor died on February 26 at age 39, and the New York City Office of the Chief Medical Examiner confirmed to People that the cause of death was complications of diabetes mellitus. Sources told the magazine Trachtenberg had recently undergone a liver transplant and may have suffered complications from that operation.
In an Instagram tribute at the time, Gellar paraphrased her vampire-slayer character, writing, “Michelle, listen to me. Listen. I love you. I will always love you. The hardest thing in this world, is to live in it. I will be brave. I will live… for you.”
Buffy costar Nicholas Brendon eulogized Trachtenberg at the time in a now-offline Facebook video, per Entertainment Weekly. “When we were working together, she was just, like, a beam of light,” he said. “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.”
And on Instagram, Buffy alum Alyson Hannigan said, “I am deeply saddened by the news of Michelle’s passing. She brought a loving energy to the set of Buffy. My thoughts are with Michelle’s family and friends.”