It's no doubt a tiara fit for a princess, and Kate knows how to pull it off.
Prince William and Kate Middleton left their 4-year-old son George and 2-year-old daughter Charlotte, at home to attend a reception for diplomats hosted by the Queen.
The white-tie event at Buckingham Palace in London had everyone dressed in their best.
This was the fourth time she and William have attended the party, which has diplomats from over 170 mission in the UK greeted by members of the royal family.
The prestigious affair marks the beginning of the festive season at the palace. Later in the month, the Queen will host her extended family for a pre-Christmas lunch before heading to her estate in Sandringham.
Prince Charles and The Duchess of Cornwall arrived in a different car from the expectant parents.
Camilla wore a tiara and beaded gown along with a three-strand pearl necklace to the affair.
Kate has only worn the favored tiara a handful of times, but everyone admits she looks stunning in it.
The pregnant royal wore her late mother-in-law, Princess Diana's favorite tiara to the prestigious event.
And she looked smashing it in!
The Queen Mary's Lover's Knot tiara was placed into her shiny brown hair that was pulled back into a beautiful updo.
She complimented it with a diamond necklace and pearl and diamond drop earrings.
The tiara, which Queen Mary made around 1914, is more than 100 years old. Middleton also wore it to the annual event last year.
What do you think of the tiara? Share with us in the comments.