Princess Kate impressed the Queen with a thoughtful gift when she first joined the royal family for Christmas.
When Prince William and Kate separated briefly in 2007, the Queen was disappointed.
During an official engagement in Windsor, Princess Kate recently paid tribute to the late Queen Elizabeth II.
Kate wore the same crimson double-breasted coat and black gloves she wore to William's Sandhurst graduation in 2006.
The Welsh guardsmen originally presented the brooch to the Queen.
The brooch has been replicated, and Princess Diana and Camilla have worn similar styles.