Question: Along with the Closer performer, what notable pop artist started out his career on adult contemporary radio?

Knowledge 1: Closer (Josh Groban album)
Closer is the second studio album by vocalist Josh Groban, released in November 2003. Much like his first studio album, half of this album's songs are sung in English, with the remainder sung in various other languages (Italian, Spanish and French). "Closer" was the top selling classical album of the 2000s in the US, according to Nielsen SoundScan. [SEP] Knowledge 2: Adult contemporary music
While most artists became established in other formats before moving to adult contemporary, Michael Bublé and Josh Groban started out as AC artists. Throughout this decade, artists such as Nick Lachey, James Blunt, John Mayer, Bruno Mars, Jason Mraz, Kelly Clarkson, Adele, Clay Aiken and Susan Boyle have become successful thanks to a ballad heavy sound. Much as some hot AC and modern rock artists have crossed over into each other, so too has soft AC crossed with country music in this decade. Country musicians such as Faith Hill, Shania Twain, LeAnn Rimes and Carrie Underwood have had success on both charts.
Knowledge 1: Closer (Josh Groban album)
Closer is the second studio album by vocalist Josh Groban, released in November 2003. Much like his first studio album, half of this album's songs are sung in English, with the remainder sung in various other languages (Italian, Spanish and French). "Closer" was the top selling classical album of the 2000s in the US, according to Nielsen SoundScan. [SEP] Knowledge 2: Adult contemporary music
A notable pattern that developed during the 2000s and 2010s has been for certain pop songs to have lengthy runs on AC charts, even after the songs have fallen off the Hot 100. Adrian Moreira, senior vice president for adult music for RCA Music Group, said, "We've seen a fairly tidal shift in what AC will play". Rather than emphasizing older songs, adult contemporary was playing many of the same songs as top 40 and adult top 40, but only after the hits had become established. An article on MTV's website by Corey Moss describes this trend: "In other words, AC stations are where pop songs go to die a very long death. Or, to optimists, to get a second life."
Knowledge 1: Adult contemporary music
While most artists became established in other formats before moving to adult contemporary, Michael Bublé and Josh Groban started out as AC artists. Throughout this decade, artists such as Nick Lachey, James Blunt, John Mayer, Bruno Mars, Jason Mraz, Kelly Clarkson, Adele, Clay Aiken and Susan Boyle have become successful thanks to a ballad heavy sound. Much as some hot AC and modern rock artists have crossed over into each other, so too has soft AC crossed with country music in this decade. Country musicians such as Faith Hill, Shania Twain, LeAnn Rimes and Carrie Underwood have had success on both charts. [SEP] Knowledge 2: Adult contemporary music
A notable pattern that developed during the 2000s and 2010s has been for certain pop songs to have lengthy runs on AC charts, even after the songs have fallen off the Hot 100. Adrian Moreira, senior vice president for adult music for RCA Music Group, said, "We've seen a fairly tidal shift in what AC will play". Rather than emphasizing older songs, adult contemporary was playing many of the same songs as top 40 and adult top 40, but only after the hits had become established. An article on MTV's website by Corey Moss describes this trend: "In other words, AC stations are where pop songs go to die a very long death. Or, to optimists, to get a second life."

Answer: Michael Bublé