Gaga, real name Stefani Germanotta, performed with YouTube singing sensation Maria Aragon, the fan whose Born This Way cover impressed her so much she requested a duet.
The 24-year-old invited her young fan onstage during a show in Toronto on Thursday night.
The Bad Romance hitmaker sang her new tune with Maria on her lap and looked visibly moved during the song.
She later took to her Twitter page to post a snap of herself wearing a T-shirt with Aragon's face on as she stood next to the her backstage.
The star wrote: 'Myself +10 year old Lady Maria of Winnipeg. She signed my T-shirt, she ate my heart, just like you.'