Justin's behavior in the months leading up to 'Swag,' including public arguments and highly criticized social media posts, has fueled concerns among close friends. One insider said, “He has mood swings — he’s kind of an extreme personality in that sense.”

Cobain delivered one of the best features on Bieber’s latest album, released on July 11, the highest-profile moment in the rapper’s career so far, with Cobain taking the opening verse on Swag’s title track.