She has been nominated for a medal in next month's Classical Brit awards.
Last night members of the choir - which won first prize at last year's National Eisteddfod - said the starlet was probably persuaded to join the choir on stage because of Wales' impressive male voice choir tradition.
Choir member Rhodri Hampson-Jones, of Trelogan, said: "It was the simplest thing. I went on Hayley's website and it had her management's e-mail address.
