Williams’ appearance came after Eilish and her brother Finneas played “Your Power” from her most recent album, with the siblings duetting on acoustic guitar.
There was a pause after the song ended, in which anticipation filled the air and Eilish took a seat on a stool to introduce her guest.
Before they broke out in song, Eilish asked: “Hayley, wanna sing something?” To which Williams replied: “Yes, I’m better at singing than talking.”