Prince Harry told Prince William that Kate, Duchess of Cambridge “could be friendlier” to his wife Meghan Markle.
Harry and Meghan stepped down as senior royals in 2020, before moving to the US to live.
But in 2018, when the pair were still part of the Royal Family, Harry is said to have spoken to his brother William about how Kate was towards Meghan.
The revelations were revealed in royal author Tom Bower’s newly released autobiography titled: "Revenge: Meghan, Harry and the War Between the Windsors."
Prince Harry and Prince William
Gareth Fuller
Mr Bower wrote: “Members of their family, said Harry, were not showing her [Meghan] sufficient support, respect, or friendship.
“Meghan, Harry believed, should be just as appreciated as their mother [Princess Diana].
“William’s reply was not sympathetic.”
It comes as Harry and William are set for an “epic clash of brothers”, royal expert Daniela Elser said.
Meghan Markle
PA
William is set to bring his Earthshot Prize awards ceremony to Boston, US, in December, while Harry is reportedly filming an “at home with the Sussexes” docuseries alongside Meghan which could air later this year.
Ms Elser said: "Thus the scene is set for an epic clash of brands, brothers, and approaches to public service, all of which is going to play out on every smartphone and TV screen in the world.
“Talk about bingeable content.
"If ever there will be a moment that signifies how dramatically divergent the paths that the Wales brothers have chosen are, it will surely have to be one man enjoying the spotlight at a Presidential library while the other is being paid to let cameras inside his kitchen.
"William’s awards, an initiative focused on real world efforts to tackle the climate crisis, are set to be held in conjunction with the John F. Kennedy Library Foundation.
"The iconography of this trip writes itself – we will have the 40-year-old future king striding about the place looking nothing short of world leader-like, possibly paling about with a former president or two, and all the while selling the monarchy as a dynamic and proactive institution,” she told news.com.au.