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Is it an honest mistake or just pretension? Either way, Gwyneth Paltrow is playing the name game on her oft-criticized website.

In her latest GOOP newsletter, she refers to "Piano Man" Billy Joel by his given name, "William."

Can you guess these celebs' real names?

While offering up Katie Lee Joel's recipe for "Dark Chocolate Chunk and Dried Cherry Cookies," Paltrow writes: "The summer before last, a mutual friend brought the lovely Katie Lee Joel and her husband William over for dinner. Much to my delight, she brought a fresh batch of these cookies with her. I adore the contrast of the dark chocolate and the cherries heaven."

Look back at Gwyneth Paltrow's style hits -- and misses!

So does Billy really go by "William?"

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No, his rep tells, adding: "No one calls him William."