Sia stunned shoppers when she whipped out her bank card and paid for their groceries at a Walmart in the US.
The Chandelier singer – who is known for hiding her face behind elaborate hair styles – dressed down in black trousers, a colourful jumper and a casual coat as she went undercover at the store in Palm Springs, California.
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According to local media, the Australian star did not announce who she was, but claimed that she was named Cici and explained her generosity by saying that she had won the lottery.
The singer, who wore her hair casually pulled back, calmly went from till to till, popping in her card and paying for people’s Thanksgiving shop.
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The star’s act of kindness later came to light on social media, when photos and video emerged.
A clip shared online shows a woman handing the singer some flowers, while hugging her and saying thank you.
Sia finishes up a payment then moves on to another cash register, asking: “Who’s next?”
A Twitter user named Adri Buckles shared the video and wrote: “So @Sia paid for my groceries today thank you so much!!
“The heart and beautiful soul you have for paying for everyone!!”
The fan said she was sorry for spilling the beans once she realised that the mystery shopper was actually a famous singer.
“But this kindness must be acknowledged,” she added.
Sia, who is known for hits such as Elastic Heart and Cheap Thrills, has yet to comment on her thoughtful shopping spree.