Why the Duchess of Cambridge did not wear her wedding ring?

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I have noticed in her photos after the wedding that Catherine, the Duchess of Cambridge, wife of Prince William, the Duke of Cambridge, never wore her wedding ring in public. It is quite puzzling since all ladies married into the royal family wore their wedding rings, even the late Diana, Princess of Wales, put her wedding ring all the time. But with the Duchess of Cambridge I only saw her engagement ring on her left finger but no wedding ring. I am just curious why.