Michael Buble might be living in fear for his job, after handing the microphone to  a great singer.

During a recent gig, Nashville man Andrew Zarrillo was handed the microphone from crooner Michael Buble to sing 'Fly Me to the Moon.'

Little did Buble know what was in store. His reaction to the fan's opening lyric is so great, he takes a seat on stage and lets Zarrillo finish out the song. And the crowd goes absolutely wild.

After his performance, Michael Buble makes some presumedly positive comments, but they unfortunately can't be heard over the screams of Zarrillo's girlfriend.

Have a look at the full video below.