The pair were on their way to the wedding of their close friends Emilia D'Erlanger and David Jardine-Paterson at the magnificent St Peter's Church. And photos of the royal sweethearts and the bride and groom appear exclusively in this week's HELLO! magazine.
Pick up your copy of issue number 1121 to see Kate's elegant outfit – a striking red Issa silk jersey dress with a stylish keyhole detail at the back.
There's also a report on the nuptials of Emila – who was once tipped as a possible match for William.
Also in this week's issue, Flavio Briatore and Elisabetta Gregoraci welcome you aboard their super yacht to exclusively present their new baby boy Falco Nathan. And Coleen Rooney gives exclusive fashion tips on what to wear for a summer wedding.
Plus there's the first pictures of a single Sandra Bullock, and Victoria Beckham reveals: "How Eva Longoria's friendship saved me."
Read the full stories in the new HELLO! magazine, on sale now.