'Songs of Innocence,' the new album U2 surprised fans by releasing -- for free, no less -- as part of Apple's fall 2014 product launch, may be followed by more new music in the months to come.

U2 frontman Bono teased the existence of a 'Songs of Innocence' follow-up already in the pipeline in an open letter to fans posted at the band's website, writing, "We’re collaborating with Apple on some cool stuff over the next couple of years, innovations that will transform the way music is listened to and viewed. We’ll keep you posted. If you like 'Songs of Innocence,' stay with us for 'Songs of Experience.' It should be ready soon enough ... although I know I’ve said that before ... "

As Bono alluded, 'Innocence' had a long and apparently troubled birth, including months of release dates that came and went. "I hope after listening to our new long player a few times, you’ll understand why it took so long," he explained in the letter's final paragraph. "We really went there ... it’s a very, very personal album. Apologies if that gets excruciating ... actually, I take that back. No apologies if it gets excruciating. What’s the point in being in U2 if you can’t go there?"

And while 'Songs of Innocence' won't cost you a penny if you have an iTunes account, we don't need to worry that the record isn't making U2 any money. While he stopped short of divulging details, Bono told TIME that Apple gave the band more than a splashy forum for debuting the new LP, saying, "We were paid. I don’t believe in free music. Music is a sacrament."