When William Leggatt was at work as a renewal energy developer a couple of summers ago, he received a bizarre email from a superfan of “Operation Mincemeat,” a British musical about a wacky World War II intelligence plot.

As the show outlines, the operation involved British spies dressing a corpse as a military officer, stuffing a briefcase with fake letters implying an imminent invasion of Sardinia, and then dumping the corpse and documents at sea to be discovered by the Nazis.

So the email contained a simple question: Was William a distant relative of Hester Leggatt, a prim secretary who appears in the musical and played a key role in the plot?

The show’s superfans, who meet in an online forum and are known as Mincefluencers, believed that Hester was involved in writing fake love letters that officials planted on the body to help make the plot believable — and that she deserved to be publicly honored. But William Leggatt had no idea what the email was talking about.

It was only when he started talking to family members who were closer to the great-aunt and, later, reading a document sent by the Mincefluencers, that he realized they were right. In the end, he recalled in a recent interview, the musical “opened a whole side to my family I’d never known.”

Since debuting in London in 2019, “Operation Mincemeat,” which opened on Broadway last week at the Golden Theater, has won plaudits for turning wartime espionage into a satirical musical. For William Leggatt and other descendants of the real life figures depicted onstage, it has also unearthed family secrets and brought newfound appreciation for their forebears.

In the musical, Hester Leggatt (Jak Malone, one of five cast members playing numerous parts) is depicted as an unemotional prude until she takes on the task of writing the love letters and sings a heart-wrenching showstopper called “Dear Bill.”

World War II aficionados had been aware that a secretary called Hester had written the romantic notes, potentially with help from others, since the journalist Ben Macintyre named her in an acclaimed 2010 history. But a slight discrepancy in the spelling of her surname meant that when the musical opened, the real Hester remained largely a mystery.

Once the Mincefluencers discovered the correct spelling, they set about finding Hester Leggatt’s descendants and eventually produced a 50-page document about her life, which even detailed a play that she performed in at school. The superfans also got MI5, Britain’s domestic security service, to confirm that a Hester Leggatt had worked for the service during the war.

William Leggatt said he never met his great-aunt, who died in 1995, and knew nothing of that background before receiving the email.

It was “pretty annoying,” he added, to find out decades after her death that she had played a role in a famous World War II plot because, he said, he would have loved to have quizzed her about it. Still, he said: “I don’t think she told even those close to her. She kept it pretty bloody secret her whole life.”

For other descendants of the Operational Mincemeat spies, the musical has led them to delve more into their family history or changed their perceptions of long-lost relatives.

Susie Pugh, a granddaughter of John Bevan, the official who approved the plot, said in an interview that attending the musical had rounded out her image of a man who died when she was 15. She had known him as an affectionate grandfather, she said, yet onstage he was “confident, strident” and ordering spies around.

Jessica Baldrian, a granddaughter of Charles Cholmondeley, another spy, said that her family had chatted regularly about him since seeing the show. She said it got some things wrong, including portraying him as a newt-obsessed nerd (the family could find no evidence of his amphibian fancying). But, she added, it was a musical: “You don’t expect it to be accurate.” Like many of the spy descendants, Baldrian traveled from Britain for the recent Broadway opening to see her grandfather portrayed on the New York stage.

One descendant has even become a Mincefluencer himself.

Saul Montagu said he had long known that his great-grandfather Ewen Montagu had masterminded the operation, not just because Montagu wrote a 1953 book about it, called “The Man Who Never Was.” The walls of the family’s home in Oxford also include numerous photographs, a painting and a caricature of Montagu, one of which was signed by Winston Churchill in gratitude for his service.

But Saul Montagu said that as a teenager he had thought little about his great-grandfather, who died in 1985.

That changed in January 2020 after a family outing to see the musical. He began delving into his great-grandfather’s life, first reading his book and then his unpublished autobiography and a handwritten diary from a year at Harvard in which he confessed to spending more time dancing and sourcing contraband liquor than studying.

As Saul Montagu’s fandom for the musical grew, he recalled, he joined the main online Mincefluencers group and answered questions about his great-grandfather.

The research, Montagu said, “humanized” his great-grandfather, making him far more than simply a cool tale to tell friends about. Now, he added, he has seen the musical 13 times, and even joked with Natasha Hodgson, the actor who plays his ancestor, about how they were “family.”

In interviews, six descendants of the characters said they loved the show, though not all were convinced that their ancestors would agree.

William Leggatt said of his great-aunt Hester, “for her contribution to finally be recognized, I’m sure she’d have been happy with that.” But if she discovered that a man was portraying her on Broadway, he said, “there’d have been some spluttering.”