Katy Perry put on a surprise show in Australia for a young fan with a brain tumor. The 33-year-old singer and "American Idol" judge visited Grace Moores at home this week after the 8-year-old missed her concert Monday in Adelaide due to a recent operation. Perry shared the story in a series of videos Wednesday on Instagram. The clips show the star preparing for the visit and spending time with Grace and her family. "Today is one of those days where I actually feel like a unicorn," Perry said in one video. "That's because I get to use my powers for good and meet someone named Grace who wasn't able to come to the show." Moores' sister Tiana Moores had reached out to Perry and her fans last week on Twitter, explaining Grace was diagnosed with a 6cm brain tumor this year. She tweeted about Perry's visit Tuesday. "GUYS WE DID IT! @katyperry just visited grace! She's truely amazing and such a sweet person this was truely amazing!" Tiana wrote. Perry is in the midst of her Witness world tour. She will perform Friday evening in Melbourne.