The former PR executive, 59, wore a tiara from her soon-to-be mother-in-law's collection when she married Prince Edward on 19 June 1999, but the headpiece also paid tribute to her future father-in-law Prince Philip.
Walking down the aisle at St George’s Chapel in Windsor Castle, Sophie looked radiant with her short blonde hair styled into a pixie cut and topped with the Anthemion Wedding Tiara – a diamond headpiece estimated to be worth around £1.6 million.
According to Maxwell Stone from Steven Stone: "The Anthemion tiara also pays tribute to another former monarch, as it was reportedly constructed using four pieces from Queen Victoria's Regal Circlet.
"It's also possible that the tiara serves as a tribute to Prince Philip, due to its use of anthemion - a technique used in ancient Greek times. Before he married Queen Elizabeth II, the late royal was Prince of Greece and Denmark.
"It's incredibly difficult to put a price on such a magnificent piece. I'd estimate it to be worth approximately $1.6 million (£1.25 million)."
She teamed it with a black and white pearl necklace and matching earrings, which were a wedding gift from Prince Edward, and her Samantha Shaw silk organza coat dress, which was embellished with over 325,000 pearls and crystal beads.
For her evening reception, it appears as though Sophie took off the coat to reveal a similar second V-neck gown hiding underneath, complete with long sleeves and a sparkly waist. However, her accessories remained the same.
Since her royal wedding in 1999, the Duchess has customised the diamond tiara. The Queen's dresser Angela Kelly confirmed in her book The Other Side of the Coin: the Queen, the Dresser and the Wardrobe that the headpiece was redesigned by jeweller Harry Collins for Sophie to wear at the Buckingham Palace state banquet for President Trump in June 2019.
The two outer sections of her tiara – shaped like the radiating petals which embellished ancient Greek buildings – were previously further apart, but they had been moved closer to the central diamond cluster and mounted on a new row of jewels along the band.
Sophie and Edward started dating in 1993, and the royal popped the question just before Christmas in 1998 with a three-diamond ring from British royal jeweller Garrard.
While announcing their news on 6 January 1999 at St James's Palace, the couple admitted that a solid friendship was the foundation of their relationship.
"I think we share a number of interests, we laugh a lot and we have a great friendship," said Sophie, and Edward similarly remarked: "We are the very best of friends and that's essential but it also helps that we also love each other very much."