Sam Smith pulls out of iHeartRadio Music Festival 'due to unforeseen circumstances': 'I am so so sorry'

Sam Smith accepts the award for best new artist at the 57th annual Grammy Awards in Los Angeles, California February 8, 2015. REUTERS/Lucy Nicholson (UNITED STATES - Tags: ENTERTAINMENT) (GRAMMYS-SHOW) - RTR4OQTJ

Sam Smith pulled out of his iHeartRadio Music Festival performance on Friday.

The 26-year-old singer who was set to join a star-studded lineup, which included Mariah Carey and Jason Aldean, at the T-Mobile Arena in Las Vegas canceled "due to unforeseen circumstances."

"Dear all, Due to unforeseen circumstances which transpired after rehearsal, it became clear that I’m sadly unable to perform at the iHeart Radio Music Festival in Vegas tonight," Smith tweeted.

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"I am so so sorry about this and I want to apologise to all my fans. All my love, always. Sam x."

According to Variety, citing sources, the Grammy-winner, who reportedly had been complaining that his throat was hurting, lost his voice.

Childish Gambino took the stage earlier than his original start time to fill in for Smith.