U2 surprised fans by releasing their new album 'Songs of Innocence' for free on iTunes recently. The move has evidently been supported by Apple at their recent iPhone 6 release event.

Apple CEO Timothy Cook called it the "largest album release of all time," after the Irish band performed the first track at the launch of the iPhone 6 and the new smart watch.

"Wasn't that the most incredible single you ever heard? We would love a whole album of that," said Cook.

The album appeared on the iTunes accounts of up to 500 million customers in 119 countries Tuesday afternoon. The agreement had been carefully negotiated by the band, their new manager (Guy Oseary), their label (Universal), and Apple.

It is believed that Apple paid the band and their label an unspecified amount as a blanket royalty fee and committed to a marketing campaign of up to $100 million to release the album for free.

"This is a gift from Apple to their customers. They bought it and they are giving it away," Oseary said.

"People who haven't heard our music, or weren't remotely interested, might play us for the first time because we're in their library. And for the people out there who have no interest in checking us out, look at it this way... the blood, sweat and tears of some Irish guys are in your junk mail," Bono posted on U2's website.

"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," he added.

Songs of Innocence will be available for free through iTunes until October 14, when the label will begin selling the album at stores and making it available online through streaming platforms.