By PAUL SONNE

ROSTOCK, Germany—Karin Vogel wakes up in this graffiti-pocked east German city and drives to the hospital where she is a therapist who counsels elderly people in chronic pain.

Karin Vogel is a direct descendant of an obscure German princess from the 18th century known as Sophia of Hanover. And that puts Vogel in line to inherit the British crown–after 4,972 other people. WSJ’s Paul Sonne reports from Rostock, Germany.

Everyone knows that should 85-year-old Queen Elizabeth II die, her son Charles, if living, would succeed her. Second in line is Charles’s son Prince William, whose wedding to Kate Middleton Friday will be a global media event. William’s little brother, Prince Harry, is No. 3.

Ms. Vogel, 38, holds a different distinction: By the account of some genealogists, she is the last person in line to the throne.

Ms. Vogel stands behind the many who, like her, are descendants of Sophia of Hanover, a relatively obscure German princess selected by the English Parliament in 1701 to inherit the crown. Sophia’s genes have dictated the succession ever since.

As for Ms. Vogel, the end of the line is just fine.

“I can lean back and relax,” she said in an interview, pleased at the very remote prospect of having to preside over 16 sovereign states anytime soon. “It is really very comforting that one doesn’t have to worry about Great Britain.”

Ms. Vogel doesn’t much care for castles anyway. “They’re so dark and so cold,” she says. On her first and only trip to the U.K., in 2001, she skipped Buckingham Palace.

Neither the royal family nor the U.K. publishes an official chart tracking Sophia of Hanover’s living descendants, a growing throng of Saxe-Coburgs, Hapsburgs, Romanovs and lesser lights united by their technical eligibility to someday call Buckingham Palace home.

The royal family’s website lists the first 38 successors but neglects to name the rest. A spokesman for Buckingham Palace said he doesn’t know whether the monarchy tracked all of Sophia’s living relatives. Citing limited resources, he refused to look into the matter.

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The palace may have dropped the scepter, but some American genealogy hobbyists have picked it up and run with it.

Daniel Willis, of Denver, Colo., spent about 18 years documenting the descendants of Sophia’s son, George I, for a 2002 book written mostly while he was a travel agent. Bill Reitwiesner, a computer technician at the Library of Congress who died in November, compiled a list of living heirs to the throne in 2001.

In the process, Messrs. Willis and Reitwiesner both reached the same conclusion: Ms. Vogel is at the bottom of the regal heap. She was 4,973 in line as of 2001, according to Mr. Reitwiesner’s research, though his list included Catholics, who are technically ineligible.

Mr. Willis says he is fairly confident Ms. Vogel remains last. He has all but memorized lists of descendants stored on a document in his computer.

“Once you get out there quite a ways, they really don’t care,” Mr. Willis says. Indeed, the list includes not just unknowns like Ms. Vogel, but many other royal families from around Europe, which are connected by marriage. Says Mr. Willis: “When you’re talking to someone like the king of Greece, he doesn’t really care what his place in line to the throne of England is.”

The U.K. succession rules date back to the 1701 Act of Settlement. Princess Anne, a Protestant, was destined to die with no heir, and the English Parliament wanted to prevent a Catholic from seizing the throne upon her death. So the Act of Settlement bequeathed the crown to Anne’s closest Protestant relative, Sophia of Hanover, and all her non-Catholic descendants. Illegitimate children are also out.

Those rules still stand today. According to the law, for a person to be in line for the throne, he or she must be an “heir to the body” of Sophia of Hanover. Sophia is Ms. Vogel’s great-times-eight-grandmother.

During a visit to her parents’ house this month, Ms. Vogel pored over the browning pages of a family tree compiled by her late grandmother Hedwig, as the dog, Rufus, stretched out under the table. The family lineage descends through Germany’s royal House of Württemberg.

Ms. Vogel’s 81-year-old mother, Ilse, a retired physical therapist who once was last in line herself, before having children, says the family always knew there was a connection to the British royals but didn’t know about how it ranked in the line of succession.

Nonetheless, tantalizing lore suggests the family was once closer to the throne than it feels today. Ilse Vogel recalled a tale centered on her great grandparents receiving a gift of two King Charles Spaniels from Queen Victoria and Prince Albert. The regal dogs grew old together, lounging by the fireplace secure in their status.

“People said they’re too old, and they stink, and they can’t move anymore,” Ilse recounted. Nevertheless, the dogs had to stay: They were a special present from Her Majesty the Queen.

Ms. Vogel and her mother have retained a certain fondness for British royalty. They admire the U.K.’s cultural heritage and its eccentricities, like bowler hats and afternoon tea. Ilse calls Elizabeth II “a great woman and a great queen.” As for Prince Charles, Ilse has confidence, having read his treatise on organic farming.

Still, neither would want to be queen. “Too stressful,” Ms. Vogel says.

To be sure, it’s not bloody likely that she ever will be queen. The succession procedure for the British monarchy could soon change. Parliament is debating amending the rules so that men do not come ahead of women.

Under the current procedure, if Kate Middleton and Prince William had a daughter and followed up with a son, the son, though younger, would be first in line to the throne.

If the full list were reordered now, according to such a new procedure, Ms. Vogel would potentially be moving on up. She says she’s in favor of the change, for the sake of equality. It could take a while, though, because all 16 “realms” of the Commonwealth—including Canada and Australia—would have to pass legislation to approve a change.

As for the impending wedding of Prince William and Ms. Middleton? Ms. Vogel says she’ll have to catch the reruns, because she just moved: “Unfortunately, I don’t have a TV.”

Write to Paul Sonne at paul.sonne@wsj.com

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