Green Day singer Billie Joe Armstrong spent his final minute on stage at the iHeartRadio Music Festival dropping a dozen different versions of the f-bomb, then smashing the heck out of his guitar. He was mad about the band's set being cut short — but two days later, TMZ's sources say he has entered rehab for substance abuse.

The band's rep also told TMZ, "Green Day wants to apologize to those they offended at the iHeartRadio Festival in Las Vegas." (Apologize to the guitar!)

You can watch Billie Joe go on his rant in this "f**k" heavy video, where somehow Justin Bieber's name gets thrown into the mix. Green Day's set was supposedly shortened due to Usher's set running long. You owe them now, Usher!

Sources: TMZ, Entertainment Weekly

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