When a royal gets married, it is customary for the Queen to present the couple with their own conjugal coat of arms – a joint coat of arms that unites both family’s coats of arms – sometime after their wedding. When Kate married William, the Middletons had no official coat of arms – so the Queen commissioned the College of Arms to create one for the Middleton family, or more specifically, as befits tradition, for Kate’s dad Michael Middleton, as the coat of arms is created for the male.
The Middleton Family Coat of Arms
The resulting Middleton coat of arms is a shield bearing three acorns, one for each of the Middletons’ children, Kate, Pippa and James, and a gold band in the center to honor their mother, Carole Middleton, whose maiden name is Goldsmith.
In keeping with royal tradition, the coat of arms was presented to the father of the bride just before the couple wed.
The cover of The Royal Wedding Program had William's Coat of Arms on the Front Cover and The Middleton Family Coat of Arms on the Back Cover:
William's Coat of Arms, which the Queen granted to him on his 18th birthday, was derived from those of the royal family and of his mother, Diana Spencer. The coronet, or crown, signifies royalty, and the three-pointed collar, or label, shows he's heir to the throne.
The conjugal Coat of Arms given to Wills and Kate, the Duke and Duchess of Cambridge, two years after their 2011 wedding:
In 2013, two years after their 2011 wedding, the Queen then presented Kate and William with their new united coat of arms, which has William’s on left, interlinked with Kate’s new Middleton coat of arms on the right.