The first album in five years by veteran Irish rock band U2 has been offered for free to the 500 million users of Apple's iTunes service.
The surprise announcement was made at a California event where Apple CEO Tim Cook unveiled the firm's latest iPhone and a new smartwatch.
The band also performed live at the event.
U2 lead singer Bono described the release of the 11-track album, Songs of Innocence, as "kind of mindblowing".
"The most personal album we've written could be shared with half a billion people - by hitting send," Bono said. "If only songwriting was that easy."
U2's last album, No Line on the Horizon, hit the top spot in the UK charts in 2009 and eventually surpassed the five-million-sales mark worldwide. However, Bono was quoted as saying that he was disappointed with the response and told the Guardian that year that he feared the concept of an album was "almost an extinct species".
The Irish band is famed for producing some of the landmark albums of the 1980s and early 1990s, including The Joshua Tree and Achtung Baby.
There had been some speculation this year that the band were planning a new album. However, the free release at the Apple event had not been anticipated.
Several prominent artists - including Beyonce - have released surprise albums recently, although the practice remains a novelty.
Free album releases by major artists are a rarity.
Radiohead initially released In Rainbows in 2007 as a pay-what-you-want download.
The same year, Prince's album Planet Earth was given away free to readers of the Mail on Sunday in the UK. Then, in 2010, the singer's album 20Ten was included for free with copies of the Daily Mirror and Daily Record in the UK, and with various other newspapers and magazines around Europe.
U2 have collaborated with Apple in the past. The terms of the deal for the iTunes release are not known.