Robbie Williams joined rapper Dizzee Rascal for a cameo rendition of Losing My Mind at Radio 1's Big Weekend in Londonderry, Northern Ireland.
The Take That star went walkabout at the former Ebrington military barracks which has been turned into an outdoor performance space on the banks of the River Foyle.
He received a rapturous reception from an audience of thousands which ranged from teenage to middle age.
Robbie shouted "Derry" and saluted the crowd then exchanged greetings with dancing revellers beside the main stage.
Dizzee, wearing a canary yellow T-shirt and jeans, ended with Bonkers. "I think it's time we got a little bit bonkers," he said to cheers.
Some performances at the event were cancelled because of disruption at Heathrow.
A Radio 1 spokesperson said: "Radio 1's Big Weekend kicked off on Friday afternoon in Derry-Londonderry and we've got a weekend of amazing acts and DJs ahead of us.
"Unfortunately due to the travel disruption affecting Heathrow we've had to cancel a few performances but we've still got an exciting line-up for our audiences and we're looking forward to a fantastic weekend of music."
Cancelled performances included Aluna George and Angel Haze on the Radio 1Xtra Stage.