In 1997, Prince Charles and Earl Charles Spencer had a heated argument during Princess Diana's funeral. Emily Andrews claimed that the royal made an "offensive" remark that opted Diana's brother to be mad; what could this be?

Speaking to the Channel 5 documentary titled "Secrets of the Royal Palaces," historian Dr. Tessa Dunlop mentioned that the situation must have been "absolutely horrific."

Charles Spencer and the Prince of Wales were reportedly seated at the same table with "really not quite enough people to buffer them from each other." (via Express UK)

The Daily Mail UK's royal editor, Andrews, wrote on Sunday that there was a "bad blood" between the brothers-in-law.

She mentioned that a source told her the two men were talking on the phone about the late princess' funeral arrangements.

However, the conversation didn't end well as Charles Spencer "hung up on him in anger" after saying something.

"So definitely there was love lost between two men," the editor added.

Royal biographer Robert Lacey gave an insight about the feud in his book "Battle of Brothers: William and Harry," writing that Earl Charles Spencer is adamant that his sister would have "been horrified at the idea of her sons having to endure such an ordeal."

He reportedly told Prince Charles as much.

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However, the conversation ended with Diana's brother "slamming down the phone" on the future monarch after reportedly making an offensive comment about the Princess of Wales.

Regarding the fight, Prince Charles reportedly wanted to take the long route of the funeral service as he walked along with his two children, Princes Harry and William.

However, Earl Charles Spencer disagreed with the decision. Lacey revealed that he was "already angry" on behalf of the Spencer family because Diana's funeral "had been hijacked into a royal occasion."

In addition, he opposed the idea of his nephews walking the "best part of a mile" behind Diana's coffin.

Speaking to BBC Radio 4's "Today," Earl Charles mentioned that he was "lied to and told they wanted to do it [the long route of the funeral service.]."

He added that he walked along with the royal family for 100 yards, and they would hear people "sobbing and then walk round a corner and somebody wailing."

"it was a very, very tricky time," he added.

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