Kate emerged from Westminster Abbey as Her Royal Highness the Duchess of Cambridge.
The newly-wed royal was handed the title as her husband Prince William was given the title — the highest rank in British peerage — by his grandmother, the Queen.
William, 28, will also become the Earl of Strathearn and Baron Carrickfergus, which means Kate will become the Countess of Strathearn and Baroness Carrickfergus.
All titles are a gift from the Queen and it was up to the monarch to choose which one to bestow on her grandson and his new wife.
Tradition dictates that Royal men receive a title on their wedding — and often more than one.
Buckingham Palace said in a statement: “The Queen has today been pleased to confer a Dukedom on Prince William of Wales.
“His titles will be Duke of Cambridge, Earl of Strathearn and Baron Carrickfergus.
“Prince William thus becomes His Royal Highness The Duke of Cambridge and Miss Catherine Middleton on marriage will become Her Royal Highness The Duchess of Cambridge.”
As well as a duchess, Kate, 29, is also technically Princess William of Wales.
Yes: to be a princess, she has to even give up her first name.
Catherine wore a long-sleeved, sweetheart-neckline gown with lace overlay, designed by Sarah Burton, creative director of luxury at Alexander McQueen. It had an almost 9-foot train. Her “something borrowed” was a tiara from the Queen of England.
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