Prince Harry and the Duchess of Sussex - who live nearby and whose first child was born earlier this month - also married at St George's Chapel last May, as did Princess Eugenie and Jack Brooksbank in October.
Last week, Meghan and Harry proudly showed off their son to the world for the first time in front of cameras inside St George's Hall at Windsor Castle.
Known as Ella, the bride is the daughter of Prince Michael of Kent, the Queen's cousin.
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"It is particularly meaningful to me as my grandparents, who I never had the chance to meet, are buried here".
The society event was a parade of stylish summer dresses, outlandish hats and men in morning suits, with numerous guests arriving in vintage buses for the service conducted by the Dean of Windsor, the Right Reverend David Conner. Her father is Queen Elizabeth's cousin.
At one point, one of the bridesmaids lay on the floor outside the 15th century chapel, with another losing her floral headband.
Lady Gabriella and her new husband Thomas became engaged whilst on holiday on the Isle of Sark in August 2018.
A great-granddaughter of king George V, who died in 1936, she is 52nd in line to the throne and, unlike her parents, carries out no royal duties.
The reception was being held at nearby Frogmore House, where Harry and Meghan staged their wedding dinner.