LONDON, April 23 -- Prince Harry's wedding to Meghan Markle, an American actress of African-American heritage, was a historic moment for Britain's royal family. Some say the imminent birth of their baby is, if anything, even more significant.

Due in the coming weeks, the baby will be seventh-in-line to the throne and, it is believed, the first person of mixed race in such a senior position in the history of British royalty.

"I think this baby is going to be hugely important historically because it's going to break new ground," royal biographer Claudia Joseph told Reuters.

"Whether it's a girl or a boy, it will be the first Afro-American baby to be born into the royal family."

With a black mother and white father, Meghan's ethnicity ha...