A royal expert claims that the alleged feud between Prince William and Prince Harry was spawned when the Duke of Cambridge and Kate Middleton were shocked at the speed with which Harry moved in his relationship with Meghan Markle.

Prince Harry, 34, and Duchess Meghan, 38, reportedly met on a blind date in July 2016 and announced their engagement in November 2017. They wed in May 2018.

"It was all so quick that William and Kate didn't have a moment to get to know Meghan because Harry hardly knew Meghan," Ingrid Seward, royal expert and editor of Majesty Magazine, said in the U.K. documentary "William & Harry: Princes At War."

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She added (via The Sun), "And of course William and Kate would have quite naturally thought, 'Oh she's been married before, she's older than Harry, I hope she's going to make him happy.' Anyone would think that."

Duchess Meghan was previously married to television and film producer Trevor Engelson from 2011 to 2013; they were together as a couple for a total of eight years.

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Emily Andrews, royal reporter for The Sun, alleged that Prince Harry lashed out at Prince William and Duchess Kate over their allegedly not being supportive of Duchess Meghan early in the relationship.

"I was told by a number of sources that he went ballistic," Andrews said. "He said, 'You're trying to wreck this relationship before it's even started.'"

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Royal expert Kate Nicholl concurred, "That was the moment I was told by sources close to the brothers that the dynamics changed. There was a shift and it was largely down to Harry resenting his brother. Harry supported William from the outset of his relationship with Kate, and he felt let down that he wasn't getting his brother's full 100 percent support with his relationship with Meghan."

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Prince William and Duchess Kate dated for nearly seven years before getting engaged and tying the knot.

Sources told The Daily Mail that Duchess Meghan maintained a "stony silence" throughout Prince Harry's lecturing of his brother and sister-in-law.

Duchess Kate reportedly accompanied Duchess Meghan to Wimbledon in 2018 as a "peace offering" and even brought flowers to the Sussexes' home the following day. The Duchesses have reportedly since bonded over motherhood.

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While reports have suggested that Prince William and Prince Harry have gotten along better since the birth of Prince Harry and Duchess Meghan's son Archie, rumors flew that tensions may still exist when it was reported that the Cambridges and Sussexes would stay in separate houses during the royal family's annual outing to Queen Elizabeth's Balmoral Estate.

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However, some insiders say it was simply a measure taken to save space and keep everyone comfortable in what can often be a crowded vacation home.