The couple joined the thousands of revellers as they rocked out to the ace line-up at this year's festival in Kildare.
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.