A young Katy Perry stricken with cancer got a huge surprise after she was forced to miss the star’s gig this week because of emergency surgery, when the singer herself turned up at her home to perform a short gig.

Eight year old Grace Moores was diagnosed with a brain tumour in April this year, and was scheduled for an unplanned emergency operation on Wednesday this week that left her unable to attend Perry’s gig on Monday (July 30th) in her hometown of Adelaide for which she had tickets.

Perry, who’s nearing the end of her massive Witness world tour and is currently in Australia, caught wind of her young fan’s plight when Moores’ older sister Tiana tweeted about it to her small followership.

A post shared by KATY PERRY (@katyperry) on

“My baby sister is meant to attend @katyperry concert in Adelaide this year but was diagnosed with a 6cm brain tumour and has been battling all year,” 16 year old Tiana tweeted with the hashtag #HelpGraceMeetKatyPerry. “Grace has been Katy’s biggest fan since she was 3, please help us try and get in contact with @katyperry.”

It quickly blew up, getting 20,000 re-tweets, with Perry arriving at the little girl’s home with a couple of backing musicians two days later to perform three of her hits, including Grace’s favourite ‘Roar’, in a show shared with her massive Instagram following.

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Introducing the video, 33 year old Perry 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.”

Having kept the show a secret until the day itself, afterwards, Tiana wrote: “GUYS WE DID IT! @katyperry just visited Grace! She’s truly amazing and such a sweet person… I just tried to do a little bit to get Grace to have fun. It was amazing to have no status and then to have Katy Perry here.”

Their mother, Marie Moores, added to BBC’s Newsbeat: “Even through all of this, it was like ‘I want to get better to see Katy’. It was the one thing she had been looking forward to for so long.”

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