Prince William reportedly hit the roof after King Charles III and Queen Camilla suggested Kate Middleton make a surprisingly personal change as she prepared to join the royal family — altering the spelling of her own name.

According to royal biographer Christopher Andersen, William considered the request so offensive that he stepped in and shut it down himself.

The bizarre clash is detailed in Andersen’s book, “Kate! The Courage, Grace, and Power of the Woman Who Will Be Queen,” which claims Charles and Camilla worried there were simply too many royal names beginning with the letter “C.”

At the time, both Charles and Camilla had royal monograms featuring interlocking C’s beneath a crown. When Catherine Middleton entered the picture, Andersen claims the couple feared yet another “C” royal cypher would be too much.

Their proposed solution was simple — but apparently infuriating to William.

“Would Kate mind if she changed the spelling of her full name from ‘Catherine’ to ‘Katherine,’” Andersen wrote.

William allegedly did mind.

The prince was reportedly “fuming” and viewed the suggestion as an insult not only to Kate, but to her entire family.

Andersen wrote that William believed the request was “nothing less than ‘insulting’” and personally pushed back against his father.

Kensington Palace told Fox News Digital that it does not comment on books.

Andersen said the unusual dispute offered a revealing glimpse into just how seriously the royal family takes appearances, symbolism and branding.

“The entire nature of Charles and Camilla’s request — that Catherine was adding too many C’s to the royal crests — shows just how much image and branding means to members of the royal family,” Andersen told Fox News Digital.

He described the monarchy as a world where even seemingly tiny details can become part of an ongoing battle over status and presentation.

Andersen also claimed the incident fit a larger pattern in William and Kate’s relationship, saying William has been fiercely protective of his wife from the beginning.

According to the author, William’s biggest concern has always been Kate’s safety and well-being.

That protectiveness became particularly obvious in 2012, when topless photographs of Kate sunbathing were published in France.

Andersen said William reacted furiously, ordering palace lawyers to take legal action and reportedly wanting those responsible to face criminal prosecution under French privacy laws.

William also allegedly stepped in after the couple became parents, making sure Kate was not overwhelmed with royal duties that would keep her away from their children for extended periods.

Andersen believes Charles and Camilla may have assumed Kate would simply agree to the name change because she had earned a reputation for being cooperative and easy to work with.

But they reportedly underestimated just how strongly she felt about her real name.

Although she is known around the world as Kate Middleton, her given name is Catherine.

Andersen said Catherine personally prefers her formal name and feels deeply attached to the name chosen by her parents.

Still, the author claimed Kate did not hold a lasting grudge against Charles.

He said the Princess of Wales is “genuinely fond” of the king and may have assumed the strange proposal originally came from someone else inside the royal orbit.

Any lingering tension also reportedly became insignificant as the family later faced far more serious problems.

Andersen pointed to the cancer diagnoses involving both Charles and Catherine, saying those health battles quickly put older disagreements into perspective.

Despite Kate’s famously calm and compassionate public image, Andersen said people should not mistake her kindness for weakness.

He described the princess as having a “will of steel.”

“Kate is very secure about who she is and how she wants to be perceived by the outside world,” Andersen said.

Changing her legal name because there were supposedly too many C’s in royal branding, he argued, was simply “a bridge too far.”

British broadcaster and photographer Helena Chard also weighed in, calling the name-change idea a “nonstarter” and ultimately a “lost cause.”

Chard suggested Charles and Camilla may have been thinking from a branding or business perspective, particularly since Catherine was already widely known to the public as Kate.

Still, she said she understood why William took offense, especially because the name had been given to Catherine by her parents.

In the end, Chard said the dispute was not serious enough to become a lasting royal feud.

“They had bigger fish to fry,” she said.

Royal broadcaster Ian Pelham Turner suggested the episode could have caused a “volatile moment” between Camilla and Catherine during the future princess’s early years inside the royal family.

But he said William was there to protect her.

Pelham Turner also claimed Catherine has traditionally been careful not to upstage Charles and Camilla at public appearances, often remaining slightly behind the king and queen.

More recently, however, he believes the 44-year-old Princess of Wales has been developing a stronger public identity of her own as William prepares for his eventual future as king.

Royal expert Richard Fitzwilliams was far less diplomatic about the alleged name controversy.

“If true, it’s idiotic,” Fitzwilliams told Fox News Digital. “The idea is simply stupid. And why? Because her name began with C and theirs did!”

For Andersen, however, the strange episode says something larger about life behind palace walls.

He argued that while most people may laugh at a dispute over a single letter, royal life is built around centuries of symbols, traditions and carefully managed imagery.

From crowns and castles to coats of arms and royal monograms, Andersen said even the smallest details can carry enormous significance inside the monarchy.

“It may seem trivial to the rest of us,” Andersen said, “but to them things like this mean everything.”