U2 band-mates Bono and the Edge stunned fans when they performed 'Sunday Bloody Sunday' live in an underground station in Berlin on Wednesday.
The Irish rockers, who played several other songs, made their way to the station by train on the U2 line (U-Bahn) where they answered question asked by fans.
"U2 just performed in the my underground line of U2 Berlin," tweeted one fan.
"Just saw Bono and the Edge on my train in Berlin - crazy," added another.
'Sunday, Bloody Sunday' was inspired by the killing of 13 innocent people at the hands of the British army in Derry on Sunday January 30, 1972 - a fourteenth person died several months later.
Writing in Rolling Stone in 2010, Bono said of Bloody Sunday in Derry: "It was a day that caused the conflict between the two communities in Northern Ireland - Catholic nationalist and Protestant unionist - to spiral into another dimension: every Irish person conscious on that day has a mental picture of Edward Daly, later the bishop of Derry, holding a blood-stained handkerchief aloft as he valiantly tended to the wounded and the dying."
U2 released their 14th studio album 'Songs of Experience' earlier this month.