In the days to come, anyone wishing to criticize Meghan Markle, the American actress set to marry into Britain’s royal family, will have to contend with Tshego Lengolo, an 11-year-old black girl and newly minted monarchist.

Tshego is a child of southeast London. She has taught herself “road,” the slang emanating from the city’s grime music scene, but drops it the second she enters her apartment, a zone patrolled by her all-seeing South African mother. They squabble affectionately, for approximately the thousandth time, over whether she can be called Tiffany.

If Tshego (SEH-ho) is royal-crazy this summer, it is because Ms. Markle is biracial, the daughter of an African-American woman and a white man. When she looks at Ms. Markle, Tshego sees a version of herself, new to England, trying to find a place among its racial codes.

The precedent set by the wedding of Ms. Markle and Prince Harry next Saturday is often played down. White royalists, in many cases, argue that racism is no longer a serious problem in British society. (“The queen currently has an equerry,” or top aide, “who is black,” exclaimed the royal commentator Dickie Arbiter, by way of evidence.) Many blacks, for their part, say the royal wedding is a distraction from the rise of intolerance and anti-immigrant nativism in Brexit-era Britain.

But to Tshego, Meghan Markle is just flat-out thrilling.

She wants details. Is Ms. Markle’s hair naturally curly, and are there pictures? Will they hire a DJ to play at the wedding, and will that DJ play hip-hop? Tshego cannot wait for the couple to have a baby, she says, because the baby will be partly African, like herself. She hopes against hope that the baby will have black hair.

“There is nothing that racist people can do about it,” she said happily. “So they might as well get used to it.”

Tshego’s mother, Carol Lengolo, who grew up in a village in South Africa, was raised to love the British royals. Friends sometimes argue with her: Ms. Markle is so light-skinned she could pass as white, they say, and, anyway, what relevance does the royal family have in your everyday life? To these objections, Ms. Lengolo responds with a sweet, slow smile.

“For me it doesn’t matter: Her mom is African, so she’s African,” she said. “We are going to be in her corner. Because we feel like she is all alone. She needs people behind her, to say, ‘Sister, we are here, you are not alone. We are here. We are going to defend you.’ ”

New Cross, where the Lengolos live, is not a neighborhood where you would expect to find great warmth for the queen. It is the source of some of London’s most influential music — reggae, ska, punk, and, more recently, grime — and of persistently high rates of violence.

Britain remains 87 percent white. Black people made up 3 percent of the population according to the most recent census, in 2011, many of them clustered in diaspora neighborhoods like New Cross. The racial tension goes back generations. In the 1970s, New Cross saw an influx of Caribbean workers invited to Britain for construction work. White immigrants bristled, and right-wing groups, like the National Front, began to march through the neighborhood.

Not far from Tshego’s house is a monument to racial division. In 1981, a house party on New Cross Road was engulfed in flames, leaving 13 young black men and women dead. Many people were convinced that racists had thrown a firebomb in the window, but a police inquest was inconclusive and no charges were brought. Thousands of black Londoners gathered in protest, the beginning of race riots that rippled through the city.

In New Cross today, the London of the global super-rich seems both tantalizingly close and unreachable. On a recent afternoon, uniformed police constables patrolled the park outside the high school, and young women in tank tops and eyelash extensions lingered in a playground, killing time. They were the grandchildren of Jamaican immigrants, and they said racism in Britain was getting worse.

Kemi Moore, 17, her hair marcelled like a 1920s movie star, said the 2016 campaign to leave the European Union had unleashed nativist feelings in white Britain. An immigration crackdown has swept up thousands of British-born descendants of the Caribbean workers — now known as the Windrush generation — who do not have citizenship documents, stripping them of health and housing benefits.

“It brings back a lot of the things we thought we were past,” she said. As for the wedding, she gave a withering shrug. “No one in the younger generation cares about the royal family,” she said. “I feel like it’s more of a tourist attraction.”

The hype around the wedding only makes her feel more alienated. “There is always a cover-up issue they use to distract everyone from the real problem,” she said.

In the late 1990s, when many Britons were questioning the value of the monarchy, those doubts were strongest among racial minority groups and the young, parts of society that felt shut out by an “aggressive whiteness which was symbolic of an old Britain,” said Mark Leonard, the director of the European Council on Foreign Relations and an author of a 1998 paper that recommended modernizing the institution.

This summer, little by little, black neighborhoods are tuning in to the national soap opera, in part because of fascination with a distant power structure.

“It’s a bigger deal for the royal family than it is for us — it’s a big deal that they’re allowing it,” said Theresa Ikolodo, 45, an office manager, as her friend had her hair braided in a South London salon.

“Maybe they’re allowing it in the hope that it doesn’t work, so they can say, well, we let it happen, and this is what came of it,” she said. “Or maybe they’re allowing it because they realize we’ve got to get with the times, this is what he wants, let him be happy.”

Anthony Gunter, a criminologist at the University of East London, said he had been startled to discover that many of his black acquaintances — people who never before expressed even mild interest in the royal family — were caught up in Ms. Markle’s story. Afua Hirsch, the author of “Brit(ish): On Race, Identity and Belonging,” has spent much of this spring responding to queries about the wedding. She responds, cautiously, that racism remains entrenched in many parts of the British establishment. She is skeptical. She is nuanced. But still.

“Practically every black and brown person I know, this is the first royal wedding they have been remotely interested in,” she said. “Even the ones who are republicans. They just can’t help themselves. Even against their better judgment, they are just so curious about the fact that there are going to be black people there.”

Among them, craning for a glimpse of the couple as they leave Windsor Castle in a horse-drawn carriage, will be Tshego Lengolo.

She will be the one with the braces on her teeth, practising dance moves when no one is looking, lobbying to be allowed to go by her less-African-sounding middle name. (“Mom, please, this world is evil. Let me be Tiffany!”) Four years after moving to Britain with her family for her father’s job, Tshego feels at home in Southeast London, and she has a touch of its swagger.

Ms. Markle is her new cause. In the weeks leading up to the wedding, she has pricked her ears to the media coverage, bristling at any criticism of Ms. Markle, including of her clothing.

“I started getting mad, like, ‘Why are you criticizing her over the smallest of things?’” she said. “I want to tell her, ‘Don’t let anyone distract you. Don’t let anyone distract you from doing what you’re doing.’”

She expects it to be a long and difficult journey, this marriage. “You have to give props to Prince Harry for choosing her,” Tshego said. “She is brave, to be the first person to step up, even though she knows people are going to be judging her. She is brave for doing that.”

Her mother, Carol, reckons she was about Tshego’s age when her grandmother, who worked as a maid for a white family in Johannesburg, came home for the weekend and gave her a castoff as a gift: An album of Diana Spencer’s 1981 wedding to Prince Charles. At the time, Carol knew only a few English words, but she paged through the album over and over for years.

“I thought, how would it be to be in another world?” she said.

The fascination stayed with her through Princess Diana’s childbirths, her divorce and her death. Last month, on the chilly day when the third child of Diana’s older son, Prince William, was born, Carol stood outside the hospital in the cold for hours, waiting to see the newborn in his mother’s arms.

On the morning of the wedding, Tshego will embark on her own relationship with the royal family.

She would like to tell Ms. Markle about steel-pan drumming, and Afro-beat dancing, and what it is like to be a new arrival in Britain. Not long after her family moved to London, a child in her class sent her a message telling her to “go back where you came from.”

She never wants Ms. Markle to feel that way. Maybe, if she stands close enough to the carriage route on Saturday, she can convey that message.

“I know how it feels to leave countries, and leave all your friends behind,” she said. “I would give her my friendship. So that she’s not alone.”