Sarah Michelle Gellar is paying tribute to her late Buffy the Vampire Slayer co-star Michelle Trachtenberg after her death at age 39.

Gellar took to Instagram on Thursday to share photos of the pair together on Buffy and throughout their years of friendship.

“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,” she wrote, putting a twist on a beloved Buffy quote.

Trachtenberg starred on Buffy as Dawn Summers, the younger sister of Gellar’s titular character Buffy Summers, from 2000 to 2003.

Trachtenberg was found dead Wednesday, Feb. 26, by her mother in her New York City apartment near Columbus Circle just after 8 a.m. local time, police sources told ABC News.

The sources told ABC News the actress recently underwent a liver transplant and may have been experiencing complications. Trachtenberg is believed to have died of natural causes and no foul play is suspected.

An autopsy will be conducted by the medical examiner’s office to determine the cause and manner of the actress’s death.

Outside of Buffy, Trachtenberg was best known for roles in the 1996 Nickelodeon film Harriet the Spy and on the teen drama Gossip Girl from 2007 to 2012.

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