That post turned out to be permanent.

"We've toured all parts of the world, North America, the Middle East, China, Australia and New Zealand, and we're always learning something," he said.

"We know it's such a privilege to do what you love."

Naturally drawn to the piano aged about four when his family brought one into the house, Simpson discovered his talent for singing much later.

"I was studying the piano at Queen's University Belfast when I discovered I could sing," Simpson said.

"A teacher encouraged me to pursue singing so I graduated with a major in piano and singing."

The Celtic Tenors will perform classical, folk, Irish, Gaelic and pop music stacked in three-part harmonies, punctuated with banter, as part of their Australian tour this month.

While each of The Celtic Tenors have been influenced by the musical traditions from their own individual parts of Ireland, Simpson, James Nelson and Matthew Gilsenan show great flexibility in melding their voices to suit the genres.

The Celtic Tenors will also perform The Irish Songbook on their Australian tour with such classics as Finnegan's Wake, In The Gloaming, Song For Ireland, Danny Boy, The Dutchman, Caledonia and You Raise Me Up.

The Celtic Tenors have sold more than one million albums throughout the world.