duchess of cambridge
The Duchess of Cambridge looked stylish in her grey hat by milliner John BoydGetty

The Duchess of Cambridge was out on official business for the third time in less than a week, looking elegant at the Commonwealth Day service today (14 March) in an Erdem coat and a wide-brimmed hat by John Boyd. The 90-year-old milliner was also a favoured designer of Diana, Princess of Wales. It is believed to be the first time Boyd has designed a hat for Kate Middleton before.

Boyd is only one of 44 milliners remaining on Beauchamp Place in London's Knightsbridge who had premises there when he began his career. The Scotsman has made hats for three generations of the Royal family, and was chosen by Princess Dianato design the hat for her "going away" outfit as she set off on honeymoon with the Prince of Wales. The tricorn hat he created was copied the world over and became one of the most popular styles of the 1980s.

The Duchess looked stylish in her Erdem coat, which costs £2,500 (£3,576) and had an unusual lace pattern in a darker shade three-quarters of the way down. She teamed her outfit with a pale grey clutch, and a pair of diamond drop earrings, The grey theme was continued with round toe suede Winona pumps by Rupert Sanderson.

She chatted with schoolchildren lining up outside the Abbey and told them that Prince George goes "super fast" on his scooter and keeping up with him is very difficult.

The Duchess arrived at the annual Westminster Abbey service with her husband the Duke of Cambridge and Prince Harry. The Queen was accompanied by the Duke of Edinburgh and several other members of the royal family.

The Commonwealth Day service is the largest annual inter-faith gathering in the UK, and celebrated Her Majesty's commitment to the Royal Commonwealth Society as her 90th birthday draws near on 21 April.