The pretty floral piece dates back to at least 1970, when the Princess Royal was pictured at Heathrow Airport as she departed for an official visit to Canada with her mother the Queen.
It was also her choice as she left for her honeymoon with first husband Captain Mark Phillips, and is clearly a particular favourite for racing events - since she's worn it on a number of occasions over the years.
Princess Anne sported a yellow coat for Royal Ascot Ladies' Day
Anne chose an elegant yellow coat for her outing on Thursday, braving the unpredictable weather. The beautiful silk jacket is from Gloucestershire boutique Shibumi, where the Princess often shops.
She added a pretty matching hat and neutral handbag, finishing the look with pearl jewellery and nude heels.
WATCH: The royals arrive at Ascot day two
The Princess joined her daughter Zara Tindall, who looked beautiful in an Erdem dress, and the Countess of Wessex at Ladies' Day on Thursday. Sophie wowed with another racing look, too, in a palm tree printed dress from Suzannah.
The Countess also surprised by choosing to wear the same hat she wore to Prince William and Duchess Kate's wedding in 2011.
Wearing the floral brooch in 1970
Royal Ascot is one of the highlights of the royal family's summer calendar, and no doubt they are thrilled to be back at the course this year. While the Queen has so far been absent from the proceedings and there's been no traditional carriage processions, it's thought that she may attend at some point.
The monarch's racing manager John Warren has said the monarch, a keen horse breeder, is hoping to attend the Berkshire racecourse later in the week. We'll keep our fingers crossed!