By DAILY MAIL REPORTER
Duchess and Duchess: Camilla, left, and Catherine attend the Garter Day ceremony at Windsor Castle
The Duchess of Cambridge was all smiles today as she took part in the Garter Day celebrations.
Despite her heavy schedule of late, Catherine remained bright and fresh-faced as she showed off her third hat in as many days.
Waving from a carriage at Windsor Castle, the radiant newlywed wore a Philip Treacy head-piece, matched with a light blue-grey dress and matching coat.
Hat's off! Catherine showed off another stunning creation by milliner Phillip Treacy
Earlier, the Queen, Prince William and other members of the Royal Family took part in the annual Order of the Garter service.
The Garter Knights wore lavish blue velvet robes and black velvet hats with white plumes in a colourful spectacle that attracted hundreds to the ceremony held at St George's Chapel.
New appointments are announced on St George's Day but the chivalric and installation ceremonies take place every year on the Monday of Royal Ascot week, known as Garter Day.
Ceremony: Catherine, Prince William, Prince Charles and Camilla rode a carriage as fans waved flags
Two new Knights - Lord Phillips of Worth Matravers, the president of the Supreme Court, and Admiral Lord Boyce, a former head of the UK's Armed Forces, - will be invested in the Castle's Garter Throne Room then 'installed' during the service.
Lord Phillips, Britain's most senior judge, is the first president of the Supreme Court, the UK's highest court, which was officially opened by the Queen in October 2009.
Lavish: Prince William took part in the Garter Knights parade at St George's Chapel
Royal affair: Princess Anne and Sophie of Wessex all attended the family day out
Jokers: Princesses Eugenie (left) and Beatrice attended, along with TV celebrity Carol Thatcher (right) seen with her mother, former Prime Minister and member of the Order of the Garter Dame Margaret Thatcher
Admiral Lord Boyce, ex-Chief of the Defence Staff, was head of the Armed Forces at the time of the Iraq invasion in 2003, retiring later that year and he now sits as a cross-bench member of the House of Lords after being made a peer.
Recipients of the honour are chosen because they have held public office, contributed to national life or served the sovereign personally.
Gift: The Queen wore a velvet coat and matching hate with elaborate feather detailing
Ancient order: The Duke of Edinburgh, left, and Prince Andrew, Duke of York
Hat's that: A member of the Household Cavalry places his helmet alongside others on a wall near the chapel
At ease: Soldiers rest during a pause in proceedings during the Order of the Garter ceremony
The appointment of Knights of the Garter is in the Queen's gift and is made without consulting ministers.
Lord Phillips and Lord Boyce bring the total number of Garter Knights to 23. Other members of the order include former prime ministers Lady Thatcher and Sir John Major.
The Queen is sovereign of the order and a number of other British and foreign royals are additional members of the order.
The Order of the Garter is the oldest and most senior British Order of Chivalry, founded by Edward III in 1348. Membership in the order is limited to the sovereign, the Prince of Wales, and no more than 24 others
The Queen and Prince Philip walk down the steps of St George's Chapel in Windsor Castle after the Most Noble Order of the Garter service
Catherine Duchess of Canterbury shares a joke with Camilla Duchess of Cornwall and other members of the Royal family outside St George's chapel after the ceremony
Garter Day 2011, Windsor Castle