"OMG OMG OMG I can't believe it happened to me!" she wrote excitedly.
"It was such a blur, I just remember her bending down to me and my friend and I just turned for the photo and wowoowow it was the best moment ever!
"Like she posed, it's crazy I wasn't even expecting her to look at my phone or notice me in the crowd."
The picture soon went viral, with envious fans reposting it online.
The young teen was delighted with the response, writing on her Tumblr blog: "It was the perfect night."
Beyonce is currently in the midst of her The Mrs Carter Show world tour.
As she tours the globe the 32-year-old is accompanied by her daughter Blue Ivy, who has been exploring with her mother.
As well as her photobomb, the Halo singer has been making the most of the country's attractions.
On Friday, she chucked herself from the top of Auckland's Sky Tower to enjoy a terrifying 1,000ft freefall plunge.
The singer performed two jumps from the 1076 feet tall tower because she enjoyed it so much, before leaving for Australia.
This followed a tour of New Zealand, where Beyonce was entertained with a pre-show haka.
She will remain down under until November 9 before she returns to the US, where her tour closes in Brooklyn on December 22.
- Daily Mail