The "popera" band he and his wife created, Amici Forever, was riding high, having sold more than two million albums.
He had sung to royalty, the rich and famous and audiences of millions at England's FA Cup final and a Bledisloe Cup rugby match.
Then in 2006, at the height of it all, he walked away.
His daughter, Sienna, then two, had been diagnosed with an autism spectrum disorder and he was told his globetrotting lifestyle would not be conducive to her recovery.
Walking away was the easiest decision the Kiwi-born, London-based tenor had made.
"If something happens to your kids, fame and fortune don't mean jack," he says on the phone from Auckland before a promotional trip to Australia this week.
"Family is most important. I did what any father would have done."
Sewell was immediately transported from a world of limos and hotels to medical journals and hospitals as he and wife Simone tried to find the best care for their daughter.
The initial prognosis was bleak, with doctors telling them their daughter would never lead a normal life and would be better off institutionalised.
They refused to accept that and, after research, found that treatments of a gluten-free diet, vitamin supplements and a detoxification program worked wonders for Sienna.
Sewell says their daughter is much improved -- speaking and learning with the help of a one-on-one teacher aide in the classroom.
The life-shaking experience led Simone to write an inspirational song about their daughter and Sewell recorded it as the centrepiece to his new album, Believe.
"When we were putting together the songs for this album the main thing we wanted to get across was this hope for families," Sewell says.
"Every parent wants their kids to do amazingly, so Simone said why don't we write a song and call it Sienna's Song?
"There is a message in there for everyone and the key words of the song are 'be all you dare, your love's to share, embrace your fear and believe'.
"The pride we have for our kids when they come out of the womb -- it's the best day of our lives -- and our lives become secondary and the kids are number one."
As the founder and driving force behind Amici Forever, Sewell's album unsurprisingly covers similar territory -- from opera classics such as O Sole Mio and Nessun Dorma to standards such as My Way and You'll Never Walk Alone.
The popera band has folded, a casualty of too many personnel changes, but Sewell remains proud of its achievements and legacy, blazing a trail for the likes of the Simon Cowell-created Il Divo and Josh Groban.
Believe is out now.
Source: The Herald Sun
