Take That fans risked being boiled alive to catch a glimpse of the band.
The reformed boy band were filming the video for their new single Patience in a lava valley in Iceland, surrounded by steaming geysers which spurted boiling water.
To the surprise of band members Gary Barlow, Mark Owen, Jason Orange and Howard Donald, a group of hysterical Take That devotees snuck onto the set, risking life and limb to catch a glimpse of their idols.
A source told Britain's Daily Star newspaper: "It was like walking on the moon. The band expected snow, but it was all rocky terrain with geysers that threw hot water in the air whenever they felt like it.
"They had safety people on hand to brief them.
But they decided to step up security and fencing around the set after finding that fans had manoeuvred their way through. "Every measure to keep anyone from burning themselves was then taken."
Gary, 35, Mark, 34, Jason, 35, and Howard, 38, flew to Reykjavik were also amazed when fans turned up on the set as it was half a day's walk from the nearest city and freezing cold.
The source added: "The boys found it a step back to the old days when fans were popping up everywhere.
"The girls who followed them in such cold temperatures were a dedicated bunch. They made sure they said hello and kept them in a spot where they could view the day's proceedings without any danger.
