Kate looked stunning in a cream jacket (complete with Peter Pan collar) and pleated skirt, pillbox hat, boxy clutch and those patent nude L.K Bennett heels that she just can't part with.As ever, the duchess played up her elegant look with the signature tousled tresses pinned back to reveal her pearl drop-earrings. And no, there's nothing that her engagement ring doesn't go with.
Prime Minister David Cameron, Irish president Michael D Higgins, the King and Queen of Belgium will also attend - so be prepared to see more pristine looks from the duchess.
Will she re-style one of her favourite designer outfits or showcase something new? We'll keep you posted.
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MORE! Watch all the latest on the Duke and Duchess of Cambridge right here.