It was a beautiful traditional ceremony, featuring a handsome young couple who are very much in love.
So many of the elements of the wedding of her close friends Sam Waley-Cohen and Bella Ballin would have reminded the Duchess of Cambridge of her own nuptials six weeks ago.
Hours after joining the royal family at the happiest Trooping the Colour in years, Kate was showing her loyalty to Sam, an old friend.
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She rushed over to see him wed with her sister Pippa Middleton. Many of the morning-suited well-wishers were even the same, among them were Princess Beatrice and her boyfriend Dave Clark.
There was one poignant note to the joyous occasion.
Kate knows Sam through his brother Tom, her childhood from Marlborough College, who died aged 20 from cancer.
She has kept in touch with his family for years, even helping raise money for the foundation founded in his name.
In 2008 she was famously pictured falling over at a roller charity disco in aid of Tom's Ward, a unit at Oxford Children's Hospital.
Sam, a highly successful amateur jockey and businssman, is also the pal credited with reuniting Kate and William following their brief split. He threw the party, at which they reportedly patched up their relationship with a heart to heart.
And his part in the Cambridges' love story has since earnt him the title of' the royal matchmaker' in the popular press.
He had said previously he wasn't sure if the Duchess would be able to make his wedding because of her tricky schedule.
So it was a wonderful surprise when the elegant brunette slipped into the church, still wearing the dramatic black hat that had been perched on her head at Buckingham Palace.
In place of the white coat she'd worn earlier in the day, the new royal was chic in a black and white patterned dress.
It had been recycled from an outing to Boujis nightclub four years ago.
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It's a little princess!