Prince William and Duchess Kate's offspring, Princess Charlotte (3) and Prince George (4), also served as bridesmaid and page boy at their aunt Pippa Middleton's wedding to hedge fund manager James Matthews last May.
The other pageboys are Harry's godson, Jasper Dyer, aged six, and seven-year-old twin brothers Brian and John Mulroney.
With the mother and daughter being so close, it's hardly surprising that Doria has a special role on the day, set to stay with Meghan in Windsor the night before the wedding and then ride in the vehicle to the church with her.
The palace has already announced that Ms Markle is not having a maid of honour because she did not want to choose just one person from her close-knit group of friends.
Thomas first pulled out the wedding earlier this week to save his daughter from "embarrassment", following a heart attack and staged paparazzi pictures, with Kensington Palace asking for understanding and respect during this "deeply personal" time for both families.
The monarch recently gave her formal consent to the forthcoming marriage, signing a notice of approval which consented to the union of: "Our Most Dearly Beloved Grandson Prince Henry Charles Albert David of Wales, K.C.V.O., and Rachel Meghan Markle". "And there was my mom, caramel in complexion with her light-skinned baby in tow, being asked where my mother was since they assumed she was the nanny", wrote Meghan in the 2015 essay.
According to a United States celebrity website TMZ, Mr. Thomas has given his ex-wife his blessing to perform the duty. She said the media had "raked him over the coals" and "distorted his image".
That's what Meghan's sister, Samantha Markle, EXCLUSIVELY tells us, blaming Thomas Markle for causing her dad to 'crack!'
As a divorcee, with a white father and an African-American mother, Ms Markle's background has provided a source of huge interest and comment, not all positive.
Companies like BA are seeking a slice of the action as wedding fever builds ahead of the big day, when thousands of royal fans are expected to descend on Windsor.
They later divorced in 1987, but Meghan remembers how her parents "crafted the world around me to make me feel like I wasn't different but special".
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