Bono and The Edge of rock superstars U2 delighted fans when they made a surprise appearance at a charity gig.
The Irish pair played an unannounced four-song set, before just 250 people, for Mencap's Little Noise Sessions at the Union Chapel, in north London.
Referring to their bandmates, Bono joked: "Don't tell Larry (Mullen) and Adam (Clayton) we've done this."
BBC Radio 1 DJ Jo Whiley, the event's curator, said the multi-million-selling duo "were actually nervous beforehand".
Whiley, who has helped curate a number of shows to raise funds for Mencap added: "Seeing them in a situation like this, in a tiny chapel, makes people realise just how great they are - worthy of all the praise they get."
The crowd were told about some "very special guests" by organisers, but had no idea who it would be until they walked out on stage.
"The singer, Paul, is a shy guy, so please be gentle with him," Whiley told the crowd, before Bono and The Edge - real names Paul Hewson and Dave Evans - appeared.
They opened their set with Stay, moving on to Desire and Angel Of Harlem.
Their closing track was a first-time performance for the song Wave Of Sorrow - a track originally written for their 1987 album Joshua Tree.
Both men left the stage to a standing ovation.
"After they came off stage, Bono was asking me if they'd been OK and they were also wondering whether the 'new' song had gone down well," Whiley said.
The pair acted as the first warm-up act for Biffy Clyro.
Fan Simon Dowling, 20, from Newcastle, said: "I was here for Biffy Clyro. We turned up at 5 o'clock outside and got rumours it was Bono and the Edge and we were like, 'that can't be true'.
"I've used all the battery on my phone taking pictures of them."
Biffy Clyro singer Simon Neil said he had found out only on Friday morning that Bono and The Edge were to perform.
"We got to meet them earlier and they were very kind. They actually apologised to us for jumping on our show which obviously, you know, is incredibly polite," he said.
© 2007 BBC News. All rights reserved.
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