— Clarence House (@ClarenceHouse) September 27, 2013
From the Duke and Duchess of Cambridge's official website:
The Duke and Duchess of Cambridge have a new Conjugal Coat of Arms which will represent them in heraldic terms as a married couple.
Designed by The College of Arms in London, Conjugal Arms traditionally show the separate shields of a Royal husband and wife, side by side.
The Duke's shield on the left shows his version of the Royal Coat of Arms granted to him by Her Majesty The Queen on his 18th birthday. On the right, The Duchess's shield is from the Middleton family Coat of Arms, granted to the family in 2011 ahead of her marriage…
In addition to their Conjugal Arms, Their Royal Highnesses also retain their own Coats of Arms to represent themselves as individuals.