"I entered the Kathleen Ferrier Memorial Scholarship, which was worth 5000 quid ($9000) - five quid was something I was happy to get from a concert for the Welsh Society in London - this was five, zero, zero, zero. All of a sudden they gave me the prize and that was really the beginning of people noticing me."
What followed was a meteoric rise. For two decades, the 47-year-old farmer's son with the rich bass-baritone voice has forged an international solo career in roles from Mozart to Wagner the world over. Now he is to opera what crooner Tom Jones once was to pop.
He attributes his success to a combination of hard work and being in the right place at the right time early on in his career.
"I sang in Brussels, one page of music - The Speaker in The Magic Flute - and the man who ran the opera house was Gerard Mortier. He was about to become the director of the Salzburg Festival and he gave me Figaro, Don Giovanni, Falstaff, you name it, he rolled the carpet out, and if I hadn't sung that one page of music I would most probably still be a British singer."
But back to Tom Jones. Terfel has a bit of a confession: he listens to recordings by his fellow Welshman before going on stage.
"I put my iPod on and play some Tom Jones, because people around me like to hear that. And they always say, 'ooh, Bryn plays Tom Jones'. Of course I play Tom Jones! He's from Wales."
He's not after the panty-throwing adulation that has greeted Jones for the past few decades, though. "We're not celebrities. We're just doing a job, just like a postman does it."
It is easy to wonder if pop might be his secret first love. After all, it's a concert far from the scored, ornate world of opera that he calls one of his most remarkable evenings on stage. Terfel jumped at the chance to swap Wagner for The Police and appear on stage among pop royalty to perform Roxanne at Sting's 60th birthday bash in New York in 2011.
"It was one of the most memorable evenings I've ever had," said the opera superstar. Some of the planet's biggest pop stars, including Lady Gaga, Stevie Wonder and Bruce Springsteen, all gathered at the Beacon Theatre to perform music by the British rocker.
"We were all there to achieve something and we wanted to give our best performance we could possibly give."
The audience may have initially giggled at his bass rendition of the sultry ballad but he said, by the end, they had been converted.
And Terfel says he's not ruling out the possibility of appearing on Broadway should operatic work stop coming his way.
"Yes, I'd consider doing a musical. I've done worse things," he laughs. Though this year there's no fear of that happening.
"There's a French saying: 'If you want to make God laugh show him your calendar.' I think he would giggle at mine."
The normally balanced workload has taken a hit largely due to the bicentennial celebrations of operatic composers Richard Wagner and Giuseppe Verdi. "Who am I not to be part of Falstaff at La Scala in Milan or The Flying Dutchman?"
Meanwhile, Terfel is looking forward to performing in Wellington and Auckland next weekend.
He says he is forever grateful for the gift New Zealand Opera gave his father for his 70th birthday - a trip to New Zealand visiting deer and sheep farms.
"It was his dream to go to New Zealand and I was incredibly proud and grateful to your country to give my father a wonderful time and great memories."
Now he wants to repay the kindness by performing two solo recitals accompanied by the New Zealand Symphony Orchestra. Not bad for the son of a farmer who turned up to study voice with little knowledge of classical music.
Just for a moment he allows himself to think what would have happened if his Guildhall years had ended without success.
"If I had failed in Guildhall most probably I would have gone back to Wales and taken up farming and maybe 15 years down the road I would have gone and tried out on Britain's Got Talent as a sheep farmer and would have impressed Simon and his team. Maybe I would be a household name now as the singing sheep farmer."
Bryn Terfel performs with the NZSO at Wellington's Michael Fowler Centre on Friday, and Auckland's Aotea Centre on Saturday.