However, Brian's rugby star status apparently cut no mustard with the strict security staff working at the event.
An onlooker revealed how he tried to enter the stage-side viewing area during Kings of Leon's set -- but was turned back.
"He's a big fan of the band and he and Amy had backstage passes and so tried to head up to the platform area to get a better view.
"But they were turned back because the security guy claimed he didn't have the right wrist band. Needless to say, Brian wasn't best pleased!" said a source.
The pair then showed they're able to rough it with the best of them after setting up camp in one of the on-site Winnebagos, which they rented for the weekend.
The celeb couple, who'll swap vows next year, are now looking forward to a long-haul holiday shortly.
Amy, who launched her debut book Hello Heartbreak last week, told the Diary how she and Brian were going over to the west coast of America for a few weeks.