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The couple was greeting patients and staff at the Monash Children's Hospital in Melbourne when the Grammy winner broke out his guitar and began to sing classic hymn "Amazing Grace."
In a video posted on YouTube, Urban and Kidman stood in the middle of a group of patients, their families and staff members while he strummed on the guitar and Kidman sang along with the lyrics.
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The last time the superstar couple performed in public together was at the 2010 G'Day USA gala in Los Angeles, where they sang they Australian rock band Men At Work's 1981 hit "Down Under."
Following the surprise performance, Kidman jetted to China, where she was honored with an outstanding contribution award at the Shanghai International Film Festival on June 14, 2014.
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