Kate Middleton doesn't wear a tiara every day, but when she does, she makes a statement. The Duchess, who's pregnant with her third child, was spotted arriving with her husband Prince William at the Diplomatic Reception at Buckingham Palace on December 5, wearing the Cambridge Lover's Knot tiara—a favorite of Princess Diana's.
Here's Kate in the tiara last night:
And Diana wearing it during a tour of Hong Kong in 1989:
The stunning tiara was actually made for Queen Mary in the early 1900s, and was passed to Queen Elizabeth, who gave it to Diana as a wedding gift. The tiara was designed to look like one owned by Queen Mary's grandmother Princess Augusta, who married the very first Duke of Cambridge (which is William's title). This could be why it's favored by Kate, who's worn it several times before. In fact, here she is in July: