Watch Billie Eilish Transform Into Sally From 'Nightmare Before Christmas'

Billie Eilish spent her Halloween weekend performing as Sally during Danny Elfman's Nightmare Before Christmas concert in Los Angeles. Unsurprisingly, the young star's performances of "Sally's Song" and "Simply Meant to Be" with Elfman (who plays Jack Skellington in the movie) were absolutely mesmerizing, but her costume was just as captivating.

Though anyone watching the live-to-film show could see that Eilish was wearing Sally's iconic, colorful patchwork dress and donning makeup stitches, it wasn't until the pop star shared close up, behind the scenes photos of her transformation that it was clear how much time and effort went into her look.

Eilish shared a series of photos, along with clips and images of Sally from the movie, on Instagram, using a lyric from "Sally's Song" as the caption: "Oh, how i hope my premonition is wrong"

See her post below.

The singer plans to end the year with the launch of her debut fragrance, Eilish, later this month, and then will embark on a world tour to support her sophomore album Happier Than Ever in 2022. The trek will see her play Glastonbury, where she'll become the festival's youngest ever solo headliner. See a full list of tour dates here.