And as with numerous outfits worn by the Duchess, Meghan's dress has already flown off the shelves and has now sold out. Meghan looked stunning in a high-neck lace dress, by the British brand, Self Portrait, with a pair of diamond earrings.
An awaiting crowd braved the dreary London weather and gathered around Buckingham Palace to catch a glimpse of the family, who also included Princess Eugenie, Princess Beatrice, the Queen's cousin Prince Michael of Kent among others.
The lunch will be an opportunity for Markle, a Los Angeles native, to meet some of the more distant relatives ahead of her May wedding to Harry.
With Meghan Markle's sophisticated sense of style, fans began wondering what the duchess-to-be would wear on her wedding day from the moment she and Prince Harry announced their engagement in late November.
Inbal Dror was indeed approached to submit sketches for Her Majesty Meghan Markle's wedding gown after dressing many brides and celebrities around the world, such as Beyonce and the daughter-in-law of US President Donald Trump.
It's believed Meghan was given special permission to attend the festivities this year because her family are based in the USA and would otherwise be alone for the day.
Grandma's house is the place to be for the Meghan Markle and Prince Harry.
The Duke and Duchess of Cambridge arrived soon after in a separate auto with their children Prince George and Princess Charlotte in the back seat with the family's nanny Maria Theresa Borrallo.
The royals have been getting into the Christmas spirit all month long.