"Unfaithful" is a pop and R&B ballad and was inspired by the music of American rock band Evanescence.
Originally titled "Murderer", the single speaks about a woman who regrets cheating on her partner.
"Unfaithful" peaked at number six on the US Billboard Hot 100 chart.
The track was certified platinum by the Recording Industry Association of America (RIAA), denoting shipments of over one million copies.
The music video was directed by Anthony Mandler.