Due to the royal inbreeding, the “physical characteristics” associated with Madragana, the king of Portugal’s mistress, it’s believed her ethnicity stayed within the family’s genes. Most historians are skeptical of the claims, but Bridgerton decided to “take [it] in a different direction than what the history books have said happened,” according to Queen Charlotte director Tom Verica.
Source: https://www.buzzfeed.com/noradominick/queen-charlotte-a-bridgerton-story-real-life-facts