Skrillex Denies He and Justin Bieber Stole 'Sorry' Riff Amid Lawsuit

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Skrillex is firing back after he and "Sorry" collaborator Justin Bieber were slapped with a copyright infringement lawsuit over the song's hook.

"SORRY but we didn't steal this," Skrillex tweeted on Friday.

In a video posted to Twitter, the electronic music producer appears to show how the riff in question was born out of a writing session recorded with singer-songwriter Julia Michaels.

WATCH: Justin Bieber and Skrillex Face Copyright Infringement Lawsuit Over 'Sorry' Hook

In the lawsuit, singer Casey Dienel, whose stage name is White Hinterland, alleges that the popular single uses a riff from her 2014 track, "Ring the Bell."

The suit argues that the riff is "crucial to both" songs, alleging that "the specific and unique characteristics of the female vocal riff of both 'Ring the Bell' and the infringing 'Sorry' are identical."

The plaintiff is asking for an award of damages, and acknowledgment that the riff was used without permission. Dienel also wants an injunction preventing further infringement of "Ring the Bell" copyrights.

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"Sorry" is a wildly successful song for Bieber, topping the charts in 13 countries. The 22-year-old pop star's track spent seven weeks at No. 1 on the Canadian Hot 100 and three weeks at No. 1 on the U.S. Billboard Hot 100.