Alice Tan RidleyOscar-nominated actress Gabourey Sidibe isn't the only talent in the family.

Her mother, Alice Tan Ridley, is a well-known subway performer in New York City with a huge, booming singing voice. And Ridley used her vocal chords to wow the judges on 'America's Got Talent.'

To a roar of the crowd, Ridley began Etta James' 'At Last,' prompting a big smile from Howie Mendel.

"Millions of people must have gone back and forth on that subway over 20 years, how come nobody signed you?" Sharon Osbourne questioned. Watch!