Josh Groban graduated from the Los Angeles County High School of the Arts
https://www.lachsa.net/
Groban originally studied acting, but moved to singing as his voice developed. Groban attended the Los Angeles County High School for the Arts, a free public school on the campus of California State University, Los Angeles, where students receive a conservatory-style education.[5]
David Foster called Groban to stand in for an ailing Andrea Bocelli to rehearse a duet, "The Prayer", with Celine Dion at the rehearsal for the 1998 Grammy Awards.[6] Rosie O'Donnell immediately invited him to appear on her talk show.[7] Foster asked him to sing at California Governor Gray Davis' 1999 inauguration.[5][8] He was cast on Ally McBeal by the show's creator, David E. Kelley, performing "You're Still You" for the 2001 season four finale.[9]
He made his Broadway debut in 2016 as Pierre Bezukhov in Natasha, Pierre & The Great Comet of 1812, to critical acclaim and nomination for a 2017 Tony Award for Best Actor in a Leading Role in a Musical. His performance at the 72nd Tony Awards earned him two Primetime Emmy nominations, one for Outstanding Live Variety Special and one for Original Music and Lyrics for the song "This One's for You".
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I saw him on Oprah about 20 years ago. I think it was she who introduced that voice to the world. Thanks for the background.