RAPT with awe, the heir to the throne listened intently to the soaring voices of the three Catholic priests from Co Antrim who have sold more than 1.4 million CDs since November.
The Prince of Wales barely took his eyes off chart-topping trio The Priests as they performed two selections of sacred music from their platinum-selling debut album.
Having earlier spent time in the Ballyclare Concerns Centre, meeting individuals with special needs, staff of a bridal shop and members of a local historical society, the couple made their way into the small community hall packed with local residents to hear The Priests perform.
Although arriving almost an hour late in Ballyclare, the prince and duchess clearly enjoyed both the welcome and the performance, staying far longer than expected, putting them two hours behind schedule when they finally arrived at their next engagement in Belfast.
As they waited for the royal couple, the priests in clerical collars, warmed their vocal chords with a few virtuoso bars of Latin music.
After the prince and duchess were seated, one of the trio, Fr Eugene O'Hagan, the local parish priest in Ballyclare, joked that the royal couple had "diplomatically" chosen Benedictus to perform for the Prince of Wales – as it was written by the contemporary Welsh composer Karl Jenkins.
As The Priests sang the tiered opening of Benedictus, the prince listened closely, swaying slightly, before the clear voices of the singers burst into the joyful crescendo Hosanna in Excelsis.
As applause echoed across the room, the prince, reportedly a fan of their music, was the last to finish clapping the performance before quiet descended and they sang An Irish Blessing.
As more applause greeted them, Fr Eugene presented Prince Charles with a signed copy of their album.
Standing, the prince spoke warmly of the "enormous pleasure" the couple had experienced visitng the centre and hearing the music.
Prince Charles said he was "enormously touched" by the music of the trio and added: "I do hope that you have nothing but the greatest success in the future."
Speaking afterwards, The Priests said they were thrilled to have sung for the royal couple.
Father Eugene said: "This was our first Royal command performance and we were very touched by the Prince's words. It was quite a humbling experience in many ways."
Earlier, the prince and duchess had broken off from the official welcoming party, which included SDLP Social Development Minister Margaret Ritchie, to spend time greeting several hundred people who had stood for hours in the biting cold.
The crowd, largely made up of elderly ladies and school children cheered wildly, as if they were pop stars, as the couple made their way along the crash barriers at the side of the road.
Young girls filmed the prince on mobile phones as he took time to edge along the row of expectant well-wishers.
Among those who braved the freezing wind was local woman Betty Jenkins, 52, who said that she was delighted to see the Prince.
"I've heard The Priests' music on TV and it's great. I'm not surprised that they are singing for him," she said.
Another well-wisher, 66-year-old Ruth McComb, travelled from Carrickfergus to see the royal couple.
"I'm here to see my future King," she said.
"I haven't heard The Priests sing – but I've heard they are very good."