Kate, who is more than eight months pregnant, will stay at home, but William and Harry are expected to be among the congregation to watch Thomas van Straubenzee marry Lady Melissa Percy.
The Duchess' final official public appearance was last weekend when she attended the Trooping the Colour ceremony with other members of the Royal Family.
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A former model has been found guilty of murder after shooting her millionaire ex-boyfriend in his Costa del Sol home.
Some warm sunshine today, but also scattered heavy showers in the South-west.