Green Day singer Billie Joe Armstrong in rehab after onstage concert freak out

Green Day's front man Billie Joe Armstrong is entering rehab for substance abuse, a rep for the band tells TMZ.

The news comes just two days after Armstrong went ballistic in Vegas during a performance at the iHeart Radio Music Festival. He was videotaped screaming obscenities, slamming Justin Bieber and violently smashing his guitar on-stage.

The band's rep tells TMZ,  "Green day wants to apologize to those they offended at the iHeartRadio Festival in Las Vegas."

The rep adds, "The band regretfully must postpone some of their upcoming promotional appearances.“