Mariah Carey or watch online Starlet (2012) full movieMarie Curie? A not-so-common mix-up, but one that saw quite the birthday blunder.

In a tweet, author Harriet Alida Lye explained that her cousin, Siobhan, told her colleagues in England she wanted a cake with singer Mariah Carey's face on it -- a perfectly reasonable request for one's birthday.

You'd think one of the world's most recognisable pop stars would be a piece of, uh, cake for most people to organise, but in this case, Lye's cousin received a cake featuring Noble Prize-winning Polish, French-naturalised physicist Marie Curie.

"They misunderstood, and [this] is the cake they made her instead," Lye wrote. "It's Marie Curie, looking very festive."

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Carey, not Curie, even responded to the mix-up on Twitter. "This could've been me if only I hadn't failed remedial math," the singer joked.

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For some people, Curie's appearance was an improvement (we like both of these famous people, so no shade on either, thanks).

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UPDATE: June 18, 2019, 8:46 a.m. AEST A revised version of this article includes Marie Curie's Polish ancestry.