The X Factor judge explained that she was asked for proof of age by a shopkeeper while trying to buy wine.
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However, when she found she didn't have any form of identification on her, she picked up a random celebrity magazine to prove who she was.
"I didn't have my ID so he wouldn't give it to me," she told The Sun.
"There were all these mags with me on the front cover so I pulled out one, slapped it on the desk and said 'Look, there's my ID'.
"'Can I have the wine?' He gave it to me," she added.
Contostavlos is set to make a guest appearance on this year's Britain's Got Talent.
The former N-Dubz singer recently stated that a duet with Voice UK mentor Jessie J will "definitely" happen.
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