King Charles III and Queen Camilla requested Kate Middleton — who spells her name Catherine — change her name ahead of her wedding to Prince William, according to a new biography.

“Charles and Camilla each had a royal monogram that consisted of interlocking C’s beneath a crown,” Christopher Andersen explained in “Kate! The Courage, Grace and Power of the Woman Who Will Be Queen.”

The author alleged Charles, 77, and Camilla, 78, were concerned a third royal cypher — a personalized monogram or emblem representing a royal family member — with a C “was overkill.”

The duo reportedly asked Middleton, 44, whether she minded changing the spelling of her first name from “Catherine” to “Katherine.”

Andersen wrote in his book, out Tuesday, that Camilla pointed out Middleton was already known to most of the world as “Kate.”

Middleton was reportedly “offended” by the inquiry.

A “fuming” William allegedly replied on his then-fiancée’s behalf, calling the request “insulting … not only to Kate but to her entire family.”

The matter was subsequently dropped, according to Andersen.

Reps for Charles, Camilla, William and Middleton have yet to respond to Page Six’s requests for comment.

William and his now-wife walked down the aisle at Westminster Abbey in April 2011, six months after their engagement.

Another wedding tidbit highlighted in Andersen’s book includes William knocking back half a dozen Cuba Libres the night before and “reeking” so strongly of alcohol the next morning that Prince Harry “handed him a mint.”

Additionally, William reportedly wanted to be bearded during his nuptials but was forbidden as there was still a ban on beards in the military, which wasn’t lifted until 2024.

After the ceremony, Harry allegedly gave an “eye-opening” speech at the reception.

According to Andersen, the Duke of Sussex, 41, spoke about “an American fan who promised to make a special wedding gift for Kate — an ermine thong, which Harry proudly held aloft to a collective gasp from the guests.”

As for the bride’s reaction? She started laughing, which prompted everyone else to join in.

Harry reportedly ended his speech on an emotional note, saying his and William’s late mother, Princess Diana, would “have loved” to attend the wedding — and would “have loved Kate.”

The couple celebrated their 15th anniversary last week by sharing a sweet photo of themselves with their three children: Prince George, 12, Princess Charlotte, 10, and Prince Louis, 8.