Fans rushed to Twitter to heap praise on the 17-year-old as she sung her own track, Love Says, for the judges.
Grace stole the show as she revealed she was mostly a "bedroom singer" and her adorable grandparents recalled how she used to sing songs from Disney's The Jungle Book.
During her audition it was only singer Tom Jones who turned round for Grace, meaning she automatically joined his team.
But after she finished all the judges heaped praise on her and were blown away when she told them she had actually written the song herself.
Tom, 78, said: "If you can write songs like that then I'm so glad I turned. I'm thrilled to bits".
Fellow judge Will.i.am asked Grace where she'd got the inspiration for the song from, prompting her to reveal that she'd never had a boyfriend.
"The moment you actually get your heart broken you're going to write the awesomest music ever," Will.i.am told her after her performance, before joking: "I look forward to it."
Backstage, host Emma Willis told the teenager that she was the first contestant to get through the auditions round with her own song.
Fans of the show were also impressed with Grace, tweeting their support for the young star.
One wrote: "I'm so happy Tom turned for Grace!"
While another user said:"grace is probably the sweetest girl ever on the show."
One tweeted: "well done Grace your very brave singing your own song but you did it."
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