Only one person will gain a new title at Westminster Abbey on Saturday, and it won’t be King Charles III, who became sovereign when his mother breathed her last at Balmoral, long before sacred oil from Jerusalem will be slathered on his monarchical forehead. Charles and Camilla, lovers for more than half a century, will reign together, after all. The House of Windsor has its surprises, yet. 

Tomorrow the woman formerly known as Camilla Parker Bowles will be elevated to queen from queen consort, sharing a title, if not the stature, of her mother-in-law, Queen Elizabeth II. It is a startling rise for the duchess of Cornwall, a woman whose great-great-grandmother, Alice Keppel, was the favorite mistress of King Edward VII. He too, like Charles, was prince of Wales before he reigned. 

That reality jumped from life to art on season 4 of Netflix’s “The Crown,” where Emerald Fennell among others plays the future queen in the throes of her affair with the married prince of Wales. Sipping red wine and dragging on a cigarette, she tells her paramour in an artfully written scene, “If you put me in a popularity contest” with her, “I will lose,” and that “someone like me has no place in a fairytale.”      

By her, of course, she means Princess Diana, her universally beloved rival for Prince Charles’s heart.

Camilla Shand and the future King Charles III first met in 1970, at a polo match held at Windsor Great Park. Their romantic relationship ended — temporarily — when the prince went off to the Royal Navy and Ms. Shand married Andrew Parker Bowles. She soon reignited things with the prince of Wales, a state of affair(s) that persisted well after his storybook 1981 marriage to Diana Spencer, though by some accounts the couple took a break of sorts for several years. 

It was in regard to Ms. Parker Bowles that the princess of Wales, Diana Spencer, once said, “There were three of us in this marriage, so it was a bit crowded.” She also called Ms. Bowles a “Rottweiler,” and in the dissolution of the marriage between the prince and princess of Wales it was Camilla who was adjudged the “most hated woman in Britain.” To ever imagine her as queen was a stretch. 

Archival footage from “Diana: In Her Own Words” shows the princess of Wales confessing, “I went to the top lady” — the queen — “I was sobbing and I said, ‘What do I do? I’m coming to you — what do I do?’” The monarch replied, “‘I don’t know what you should do. Charles is hopeless and that’s it.’” 

In 1989, there was a notorious phone conversation between Ms. Bowles and the prince of Wales, secretly recorded, where the latter told her, “I’ll just live inside your trousers or something. It would be much easier.”

Diana added that she said to her husband, referring to Camilla, “Why is this lady around?” She alleges that he retorted, “I refuse to be the prince of Wales that never had a mistress.” They divorced in 1996, and she died in a Paris tunnel the following year. 

A poll conducted in 2006, the year after she and King Charles married, found Ms. Parker Bowles’s approval rating to be 21 percent: She inherited Diana’s husband, but not the late princess’s magic touch with the public. A Daily Mail poll from February, though, disclosed that 55 percent of Britons support her elevation to queen. She is aging well, with a slow motion happy ending in sight. 

The soon-to-be-queen will not be the first woman with that title who traces an unconventional path to the throne. England’s two greatest — the two Elizabeths — could not have expected to sit on the throne. Elizabeth I only acceded to the throne after the death of her half-brother Edward and her half-sister Mary. She was an afterthought to her father, Henry VIII, who lusted after a son. 

The second Elizabeth, crowned in 1953, could not have expected to wear the crown, either. The eldest daughter of the duke and duchess of York, she was ticketed for junior royalty before her uncle, ​​King Edward VIII, abdicated the throne, driven by love for the divorced socialite Wallis Simpson. Elizabeth Windsor’s father became King George VI, and the orb and scepter passed to her. 

The queen consort’s popularity is climbing as another once-divorced royal — the duchess of Sussex, Meghan Markle — is embroiled in cascading controversy. She will not be attending the coronation, electing to stay behind at the Montecito manse she shares with Prince Harry. The Sussexes have accused the queen consort of orchestrating a press campaign against them. 

In his memoir, “Spare,” Prince Harry reports that he “begged” his father not to marry Ms. Parker Bowles, and pegged her as a “wicked stepmother.” He told Anderson Cooper that his stepmother is “dangerous” because of her ties “within the British press” and that “with her on the way to being queen consort, there was gonna be people or bodies left in the street.”

In a 2015 interview with CNN, King Charles reflected regarding Ms. Parker Bowles that, “It’s always marvelous to have somebody who, you know, you feel understands and wants to encourage. Although she certainly pokes fun if I get too serious about things.”

The crowns will be placed on the heads of the new — although not young — monarchs even as rumors of Elizabeth II’s displeasure persist from beyond the grave. The Spectator reports one intimate of the royals confiding, “At the drinks before the dinner, a small group were talking to the monarch and she explained that Harry meeting Meghan had become a complete catastrophe and described her as evil.”