By Lara Walsh
Updated May 16, 2016 @ 9:00 am
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Britain's Kate, the Duchess of Cambridge, attends the televised celebration of Queen Elizabeth II's 90th birthday in the grounds of Windsor Castle in Berkshire, Sunday May 15, 2016.
Credit: (Chris Jackson//PA/AP

The royals gathered Sunday at Windsor Castle to celebrate Queen Elizabeth with a very special 90th birthday event, which included performances and appearances by Helen Mirren, Kylie Minogue, James Blunt, and Shirley Bassey, but as usual Kate Middleton stole the show, turning heads with her stunning but effortless style.

Catherine, Duchess of Cambridge, proved that although she's now a seasoned royal, she still can work a high street piece into any occasion. She wore a less-than-$100 red Zara coat with a Peter Pan collar, raglan sleeves, and two oversize buttons, over a $5,995 Dolce & Gabanna white lace dress with long sleeves and a tiered skirt to the event.

Catherine, Duchess of Cambridge attends the final night of The Queen's 90th Birthday Celebrations being held at the Royal Windsor Horse Show in Home Park on May 15, 2016 in Windsor, England.
Credit: Max Mumby/Indigo/Getty Images

Kate paired the elegant look with a sleek braided updo, which showed off diamond teardrop earrings. And to top it all off: The bright red color of her coat matched the accents on Prince William and Prince Harry's uniforms.

Prince William - Prince Harry
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Further proof that the duchess still has the street style game down to a science? She joined Prince William and Prince Harry in London Monday to launch their Heads Together campaign and the 34-year-old opted for a chic patterned Banana Republic skirt, a cream blouse, navy heels, and of course her enviable trademark blown-out locks.

Prince William and Catherine, Duchess of Cambridge attend the official launch of Heads Together at The Olympic Park on May 16, 2016 in London, England.
Credit: Neil P. Mockford/GC Images

To launch the Heads Together Campaign in London with Prince William and Prince Harry, the duchess wore a cream blouse, a patterned Banana Republic skirt, and navy heels. She even put on boxing gloves to promote the benefits of physical activity for mental health.

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