The idea that a scion of the former colonies would be seventh in line to succeed Queen Elizabeth II to the throne could change the royal family from within - and help extend a surge in popularity for the monarchy.
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The child of the Duke and Duchess of Sussex - Meghan Markle became a duchess when she wed Prince Harry a year ago - is due very soon.
Baby Sussex, as the child is known ahead of its birth, will be a product of two cultures: its father a prince who is a symbol of Britain; its mother quintessentially American - a self-made TV star with a white father and an African American mother.
The child is unlikely to ever become king or queen, but the presence of a half-American child who may choose to hold dual nationality could shake up the royal family, just as the arrival of Meghan has had a modernizing effect on the stately but sometimes stodgy House of Windsor.
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"It's quite possible the child will have a lot of American influence," royal commentator Hugo Vickers said. "The royal family is not totally unused to that kind of thing. Children have been born with Greek mothers or German mothers in the past, obviously, but Meghan is the first American mother so close in the royal family."
Certainly, Meghan isn't following any of the royal scripts when it comes to childbirth preparations.
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Unlike Harry's brother Prince William and his wife Kate, Harry and Meghan have chosen to keep the details about their baby planning private, despite - or perhaps because of - intense media interest in the baby's arrival, expected in the next few weeks.
The couple hasn't revealed where Meghan intends to give birth, so there isn't likely to be a 24/7 media stakeout outside the hospital as was the case for the births of William and Kate's three children, Prince George, Princess Charlotte and Prince Louis.
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Don't expect a photo of the happy family walking out of the hospital looking picture perfect hours after the birth either - Harry and Meghan have said they want to celebrate privately with their extended family before telling the world a baby has been born.
Palace officials accustomed to having a role in choreographing the coverage of major royal events are concerned that Harry and Meghan may announce the birth on their brand-new Instagram account - and give the public its first glimpse of the baby via Instagram as well.
Harry faces less pressure to conform to royal protocol than William because of William's role as a likely future king: he will follow his 70-year-old father Prince Charles to the throne.
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That also makes the baby's American parentage less of a pressing issue, since it would take a series of tragedies to hit William's children for Baby Sussex to become monarch.
That hasn't kept the British media from speculating that Meghan will choose an American as a nanny - Mary Poppins be damned! - and possibly even put a man in that crucial role. Some believe Meghan will insist on dual citizenship for the child, a status that is allowed by both countries.
Joe Little, the managing editor of Majesty magazine, says many people have no issues with evolving traditions in the monarchy.
"Our royal family, like all the other European royal families, are no longer marrying within royal families, so this is inevitable, and many would say a good thing," he said.
PHOTOS: Prince Harry, Meghan Markle through the years