Mr Scobie and Ms Durand, said: “Although Meghan tried to make eye contact with Kate, the duchess barely acknowledged her.”

Mr Scobie told the Times: “To purposefully snub your sister-in-law… I don’t think it left a great taste in the couple’s mouths.”

The royal authors describe heightening tensions between the Sussexes and other members of the Royal Family and claim the couple felt as though they weren’t being listened to by the old guard, who a friend of the couple’s described as “vipers”.

They say the Sussexes felt their complaints were not taken seriously and believed other royal households were leaking stories about them to the press.