According to a royal author, Prince Harry was displeased and felt left behind when Prince William started spending more time with the Middleton family after marriage and the birth of his children. Their close-knit family unit left Prince Harry feeling cast out as Prince William started to spend more and more time with his in-laws and less time with his brother.

In her book The Palace Papers: Inside the House of Windsor, the Truth and the Turmoil, author Tina Brown cited a former aide who claimed that the brothers’ "relationship hadn’t been the same since William married Kate".

Ms Brown wrote, "Though they were still incredibly close, living next door to each other [at Kensington Palace], sharing the same office, and hanging out an awful lot", she claimed Harry "mourned his us-against-the-world bond with William".

The author adds: "Harry felt displaced by their bougie family unit, and couldn’t understand his brother’s obsession with his Middleton in-laws, whose Bucklebury world bored Harry to tears. The [Waleses] had become a tight unit, and William a full-on Windsor country bumpkin.

"On weekends when he wasn’t chez Middleton, he was tramping the grounds of Anmer Hall, the red-brick Georgian mansion on the Sandringham Estate that the Queen gave the couple as a wedding present, wearing a flat cap and tweed jacket like his 'turnip toff' Norfolk farmer friends."

The author also writes about Prince William's possible views about his younger brother, Prince Harry. She claims: "He was less amused than the British public by either the strip billiards debacle in Las Vegas or Harry’s ceaseless boozy nightclub forays with his rowdy friends. His younger brother’s recklessness exasperated him."

Joe Little, Managing Editor of Majesty Magazine, said: "William fitted into the Middleton family very quickly and they took to him as a future son-in-law."

"I think also a bit of stability and grounding and a bit of normality that William perhaps wasn't too familiar with when growing up because clearly his parents' marriage was facing difficulties when he was a child and he was very aware of that and eventually their marriage disintegrated.

"With the Middletons, he got stability and a bit of normality, so for that William will forever be grateful."