Buble is known for sharing the microphone with random fans, but it's never planned.
It was Erin Bellucci's turn to take the mic at Madison Square Garden Wednesday night.
Bellucci's sister had her camera ready.
The UDel junior belted out the cover Etta James' 'At Last' in perfect key, wowing the crowd and Buble himself.
As luck would have it, Ryan Seacrest was in the crowd, so maybe we'll be seeing Bellucci on American Idol.
Seacrest and Kelly Ripa spoke about Bellucci's performance on Thursday's episode of "Live with Kelly and Ryan."