WATCH: Katy Perry makes sick fan's dream come true after visiting her at her home

She's one of the biggest superstars in the world of music, but Katy Perry used her fame in the most positive way possible earlier this week. The 'Firework' singer visited an eight-year-old girl called Grace Moores after she was unable to attend Katy's show in Australia due to having brain surgery.

Grace, who has been a MASSIVE Katy Perry fan since the age of three, was diagnosed with a 6cm brain tumour in April, meaning she was unable to see her idol in concert. Grace's sister Tiana set up an online campaign after the diagnosis, in the hope her little sister would get the chance to meet Katy.

After Katy and her team heard about little Grace, the 33-year-old showed just how big her heart is by setting up a private concert at Grace's home in Adelaide, Australia.

Katy has since posted a number of videos of herself surprising Grace as she says, "Today is one of those days where I actually feel like a unicorn. That's because I get to use my powers for good."

Watch the heart-warming moment below:

As Katy was greeted by Grace and her family in Adelaide, the singer asked the youngster what her three favourite songs were. She then performed 'Roar', 'Chained To The Rhythm' and 'Firework' with her acoustic guitar, as Grace and her family enjoyed the show.

😍😍😍

After Katy uploaded the video to her Instagram page, fans were quick to comment, praising her for her kind act.

One user wrote, ' This is amazing!!! So kind ❤️', with another adding, 'What an amazing person are you!!!!! Crying non stop ❤️❤️❤️❤️❤️❤️❤️. A third then added, 'You are so amazing 😍💜🦄 love you 😘'. sic

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We love Katy! ❤️

You can hear Katy Perry's biggest hits on the Hits Radio playlist!

• Katy Perry