Former Cathedral School pupil and star of Only Men Aloud, David Mahoney took time out of rehearsals for the choir's up and coming American tour this week to go back to school.
A Dean's Scholar for two years at Llandaff Cathedral and an Oxford music graduate, David was tasked with being Simon Cowell for the evening to judge the School's House Singing Competition.
Themed on Songs from the Musicals, the three Houses - Dyfrig, Euddogwy and Teilo, named after the Llandaff Saints - wowed the audience at the Reardon Smith Theatre in Cardiff with a mix of House Choir and A Capella performances from more than 90 pupils.
A medley from Grease the Musical, in true T-Bird and Pink Ladies fashion kicked off the event, followed by performances from musicals including We Will Rock You and Rent.
Judged against six criteria, only one point separated first and second place, with Dyfrig announced as this year's winners, followed closely in second place by Euddogwy and Teilo in third.
Mr David Mahoney said: "This event was a fantastic showcase of musical talent, which made my job as judge very difficult!
"For me, there's nothing better than performing in front of a live audience and it was very refreshing to see so many young people gain so much pleasure from singing and they should all be very proud.
"If it wasn't for the musical training I received at the Cathedral School, I wouldn't be where I am today and I hope that this competition becomes a permanent fixture on the School calendar."