While eyes may have been on the newlyweds, Saturday's appearance was all about William's grandmother, Queen Elizabeth II, who was honored with the "Trooping the Colour" ceremony, a celebration of the monarch's official birthday. The event marked the 85th birthday of the Queen, who has reigned since 1952.
Her first ceremonial event as the Duchess of Cambridge began when Catherine, wearing a double-breasted cream jacket by McQueen and a black hat, made her way from Buckingham Palace to the Horse Guards Parade in Whitehall in a horse-drawn carriage, waving and smiling to the crowds on London's Mall, much like she did on her wedding day. Except this time William was not by her side. He was participating as an honorary colonel on horseback.
Sitting next to Camilla, the Duchess of Cornwall, Catherine chatted and giggled on the short journey with Prince Harry and Prince Andrew, the Duke of York, riding with them.
As the mounted band played the national anthem and to cheers from the thousands that had gathered, the Queen appeared in a carriage alongside Prince Philip, while William rode the Household Division charger Wellesley behind them.
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It is the first time that William has taken part in the historical procession. Dressed in the red uniform of the Irish Guards, the same one he wore on his wedding day, he also wore the famous bearskin hat, making him almost unrecognizable.
During the Horse Guards Parade, Catherine watched the Queen take the salute and review her immaculate troops as the Colour – a regimental flag – was paraded in the ceremony, which dates back to the 18th century.
On the way back to Buckingham Palace for not one but two balcony appearances, the Duchess of Cambridge seemed completely at ease, smiling and waving as she arrived in the her carriage.
"She smiled right at me and waved," said Rita Pike, 69, from Essex. "I think people have taken her to their hearts because she seems so genuine."
On the balcony, the royal family, including the Queen, joined William and Catherine to watch a flyover by military aircraft.
"I was overwhelmed," said Lorraine Smith, 25, from London. "In the flesh, Kate is absolutely beautiful and she is embracing her role so well."