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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David Cameron will say the Tories are the party of the "grafters, roofers, retailers and plumbers" as he set out plans to help small firms
Lib Dem leader Nick Clegg will say his party are fighting '60 Eastleighs' on the campaign trail in the Hampshire constituency today.
The late Coronation Street actress Anne Kirkbride has been nominated for a British Soap Award.