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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Nine months on, Stratford - where the referendum vote was 52:48 - remains as divided as ever over whether leaving the EU is a good idea.
A remarkably mild night with misty low cloud on the hills of Scotland, Wales and north-west England and further rain in places.
There's a wider purpose to Prince Charles' nine-day visit to Romania, Italy, Austria today.