Kate Middleton wore a diamond tiara that hadn't seen the light since the 1930s.

Middleton, 41, attended a state banquet Tuesday night at Buckingham Palace in London hosted by King Charles III and Queen Camilla in honor of South Korean President Yoon Suk Yeol and first lady Kim Keon Hee's state visit to the United Kingdom.

But one accessory captured the public's attention: the dazzling diamond tiara atop the head of the Princess of Wales that she had never before worn publicly.

Named the Strathmore Rose Tiara, the stunning floral headpiece remained in the Windsor vault for almost a hundred years until Tuesday's banquet.

It is the fourth tiara Middleton has worn since she tied the knot with Prince William and joined the royal family, having previously donned the Cartier Halo tiara, the Lotus Flower tiara, and the Queen Mary's Lover's Knot tiara for special events.

(Photo : Getty Images/Yui Mok/POOL/AFP )
Britain's Prince William, Prince of Wales (L) and Britain's Catherine, Princess of Wales arrive for a a State Banquet at Buckingham Palace in central London on November 21, 2023, for South Korea's President Yoon Suk Yeol and his wife Kim Keon Hee on their first day of a three-day state visit to the UK. South Korean President Yoon Suk Yeol and First Lady Kim Keon Hee began a three-day trip to the UK on Tuesday, with King Charles III's hosting his first state visitors since his coronation.

It originally belonged to Queen Elizabeth, the Queen Mother, who received it as a wedding gift from her parents. Her father was the Earl of Strathmore and Kinghorne. Hence, the name of the tiara. 

According to The Court Jeweller, British art historian and curator Sir Hugh Roberts pointed out that while the acquisition of the piece dated back to the 1920s, its origins traced back to late 19th-century England. Additionally, he disclosed that the detachable flowers, initially designed to be interchanged, were originally replaceable with five collet-set sapphires.

The tiara passed to Queen Elizabeth II from her mother in 2002. However, throughout her lifetime, the Queen never publicly wore it.

Middleton is only the second person to wear the Strathmore Rose tiara in public despite numerous speculations in the past that one of the royal brides might wear it for her wedding.

Lauren Kiehna, founder of The Court Jeweller, told People that the Princess of Wales has consistently indicated her desire to mirror the royal role of the Queen Mother.

"Kate has always signaled that she'd like to emulate the Queen Mother's royal role, and wearing her jewels is an important symbol of that continuity," Kiehna said. "It's fitting that Kate -- likely with some assistance from King Charles --would choose to wear the tiara exactly a hundred years after the Queen Mother originally received it."

Middleton paired the Strathmore Rose tiara with a white, floor-length gown by Jenny Packham with gold embellishments on the cape sleeves. She also donned a pair of white, elbow-length gloves and diamond drop earrings from Queen Elizabeth.

(Photo : Getty Images/Yui Mok/POOL/AFP )
Catherine, Princess of Wales and Choo Kyung-ho Deputy Prime Minister of South Korea attend the State Banquet at Buckingham Palace with guests on November 21, 2023 in London, England. King Charles is hosting Korean President Yoon Suk Yeol and his wife Kim Keon Hee on a state visit from November 21-23. It is the second incoming state visit hosted by the King during his reign.

Her attire included a royal blue sash symbolizing her position as a Dame Grand Cross of the Royal Victorian Order, an honor personally granted by the late monarch in recognition of her dedicated service, according to Hello! magazine.

During the dinner, Princess Kate had a prominent position at the top table, seated alongside her husband Prince William, King Charles, Queen Camilla, and President Yoon.

(Photo : Getty Images/Aaron Chown/WPA Pool)
Catherine, Princess of Wales, President of South Korea Yoon Suk Yeol, King Charles III and Queen Camilla at the State Banquet at Buckingham Palace on November 21, 2023 in London, England. King Charles is hosting Korean President Yoon Suk Yeol and his wife Kim Keon Hee on a state visit from November 21-23. It is the second incoming state visit hosted by the King during his reign.