Prince William Prince Harry
rince William, Duke of Cambridge (L) and Prince Harry attend a Business Leaders Employment meeting, hosted by the Royal Foundation of the Duke and Duchess of Cambridge and Prince Harry at the Queen Elizabeth Olympic Park on September 10, 2014Getty Images

Seems like Prince William's advice has not gone down well with his brother. It has been revealed in a recent interview by Katie Nicholl, a royal expert.

The best-selling author was one of the panel members on TLC's 'Kate v Meghan: Princess at War? Special', and on that show she revealed that "William was quite concerned that the relationship has moved so quickly. And being close to Harry, probably the only person close enough to say to Harry, 'This seems to be moving quickly, are you sure?" said Nicholl.

And things went downhill from there, Prince Harry did not take that well and the Royal Feud between the fab four started.

"Harry is hugely protective of Meghan. He saw that as criticism. He interpreted that as his brother not really being behind this marriage, this union, and I don't think things have been quite right ever since," Nicholl said and clarifying how a bit of "well-intended brotherly advice riled Harry."

William, Harry, Kate, and Meghan
Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge, Prince Harry, Duke of Sussex and Meghan, Duchess of SussexPaul Grover- WPA Pool/Getty Images

And this feud gathered momentum ever since news of Harry and Markle, leaving Kensington Palace surfaced.

Also during 2017's Christmas, when Queen Elizabeth II herself invited the not-yet-married Meghan Markle to their family holiday, it was the first tipping point for Prince William to feel jealous of his brother. Another royal reporter, Robert Johnson pointed out, he says, "I'm sure at Christmas Prince Charles was knocking heads together and you can see that by those photographs of them all walking together in line."

Even Nicholl pointed out the same, she says, "Harry felt William wasn't rolling out the red carpet for Meghan and told him so. They had a bit of a fallout, which was only resolved when Charles stepped in and asked William to make an effort," she said to Vanity Fair.

Lady Colin Campbell, a controversial royal commentator has alleged that there have been changes in Harry after his marriage. "Everything I hear is that Harry is completely beguiled by Meghan and completely enthralled to her," claimed the 69-year-old, who alleges to have insider knowledge on the royal family," she said on the show.

The couple is not going to spend time together on their first valentine's day as Prince Harry will be reporting back to work as Captain General Royal Marines in Bardufoss, Norway.