The You Raise Me Up star, who is gearing up to make his Broadway debut, has sold millions of records worldwide and scored a number of Grammy Award nominations over the years. But he reveals his career highlight to date came in 2008, when he was invited to belt out Simon & Garfunkel classic Bridge over Troubled Water with the music icon himself.

"He was my high school hero," Groban gushed to O magazine. "I remember sitting there, hearing our voices blend, and thinking, 'Man, high five to kid self!'"

Elsewhere in the interview, Groban admits he still loves to sing in the shower, because he can put his vocals to the test without the fear of embarrassment.

"I think of the shower as a little confidence cube: It gives me the courage to sing higher than I should," he smiled.

The 35-year-old is currently preparing to show off his vocal range in his first Broadway gig in Natasha, Pierre & the Great Comet of 1812, a musical adaptation of Leo Tolstoy's epic novel War and Peace. Previews for the show begin next week (18Oct16).