In the final warm-up for U2, the sound system played Thin Lizzy. Guess who just got back today?/Them wild-eyed boys that have been away, came the tones of the late Phil Lynott, in the immortal opening words of The Boys are Back in Town.
Sure enough, when U2 took the stage, standing in the wings was Bertie Ahern.
Bertie and the Government boys have been away lately, but they were back on Saturday night, when the only town worth being in was Slane.
The Taoiseach's presence - in keeping with Phil Lynott's lyrics, he was "dressed to kill" in an off-white jacket - may have had something to do with his role in facilitating next week's second concert.
But with the economy faltering and an election looming, he may also be looking to U2 as coalition partners. The band has certainly joined the establishment in the 20 years since playing support for Thin Lizzy at the same venue.
Their latest visit attracted at least 80,000 paying customers (it was difficult to find fans who had had their tickets scanned for forgeries), with the same to come next week.
Meanwhile, invited guests were so numerous, and in some cases so unused to the rigours of rock concerts, that a huge temporary seating structure was in place to facilitate them.
Even the weather conditions demanded by the band's latest signature song - Beautiful Day - obliged, with the sun, and later a half-moon, shining on the proceedings.
Fans were as densely packed as anyone could remember, but traffic apart, the organisation triumphed over all problems.
Nothing was allowed to spoil the day. While the stage lighting dazzled fans, behind stage a different light show proceeded almost unnoticed, as 100 Garda and other personnel patrolled the river Boyne into the night, sweeping the banks with searchlights. Not even the Rio Grande gets this much attention.
The band's two-hour set was faultless, and given poignancy by the death days earlier of Bono's father.
The singer thanked God "for taking my old man away from his sickness and his tired old body and giving him another one", and pictures of the late Bob Hewson filled the screens over the stage when the group performed One in their second and final set of encores.
The crowd called for more, but as the band members were whisked away in limos, the woods behind the stage exploded into a fireworks display that left fans breathless.
Among the most breathless were the young daughters of Henry and Iona Mount Charles, who rushed back into the castle yard to recount the fireworks show to their mother.
Some children have to make do with bouncy castles, but the lucky Mount Charles kids get to live in a real one, where the world comes to visit once a year. And now, thanks to the man in the white jacket, twice.
The Taoiseach expressed the hope that "all the people who were moaning in March about the second concert will see the benefits of people enjoying themselves".
Accompanied by his partner, Celia Larkin, he chatted briefly with another guest, former Northern Ireland secretary Mo Mowlam.
Then he left early, possibly to meet the other wild-eyed boys down at Dino's Bar and Grill.
