"She looks so chic and we are fantastically happy," Sarah Marshall, manager of the John Boyd boutique in London's Knightsbridge, tells PEOPLE. The royal mom was seen entering the church in the milliner's peach bloom hat in grey with 100% silk trimming – a "classic John Boyd design," reveals Boyd's employee.
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While Boyd, who was given an MBE in 2014, was "involved in the process" and the style was "his design," other members of the millinery team were also involved in hand-finishing the royal mom's grey bespoke hat, which featured – unusually for Kate – a wide brim, angled slightly to one side. Prices of similar styles start from $716.
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And the milliner extraordinaire is used to having royal clientele. When the respected Scotsman opened a boutique in London's Beauchamp Place, he was popular among the well-heeled ladies of Knightsbridge and Mayfair, but he became a global success when Lady Diana Spencer (pre-wedding to Prince Charles) became a loyal customer. A pink tricorn hat he made for Diana in 1981 made headlines and was copied all over the world.
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In another historical tribute, Kate opted for Commonwealth-born designer, Erdem. Canadian Erdem Moralioglu shows his collections in London and has been worn by the royal mom several times before. The felt grey coat, with black lace and laser cut detailing is based on a look from the designer's Pre-Fall 2015 collection, which sold for approximately $3,580.