Kate, Princess of Wales, treats her husband Prince William "like a fourth child" due to his tendency to throw tantrums, a source who worked with them in Kensington Palace has said.
Author Tom Quinn revealed his conversations with the source, who lifted the lid on the dynamics between the two senior royals.
"Kate treats him [William] like the fourth child because he's prone to tantrums," the source told Quinn.
The former insider told Quinn that Kate has a cunning strategy for preventing arguments from escalating.
"They do have rows. It's not a perfect marriage. They have terrific rows," the author explained.
"But, where some couples have a row and throw heavy vases at each other, William and Kate throw cushions at each other. It's always kept under control."
Quinn, who penned 'Gilded Youth: An Intimate History of Growing Up in the Royal Family', said that much of William and Kate's marital success is down to the Queen's legacy of peacekeeping and her age-old motto which embodies the spirit of the Royal Family: "Never complain, never explain."
The late Queen understood the importance of maintaining a dignified silence during challenging times, Quinn told Express.co.uk.
"Because William adopts the manners and ways of behaving of his grandmother and Kate is very good at not complaining, both of them have stuck to the thing that made Queen Elizabeth II such a remarkable monarch," he explained.
The author added: "They very rarely complain and when they do it's always in measured terms."
William and Kate remain extremely popular with the British public, although Kate has recently overtaken her husband in the popularity stakes, a recent Ipsos survey found.
The Princess of Wales was the most liked at 38 percent, followed by her husband and heir to the throne, William, at 34 percent.
In the survey, 62 percent of respondents said they were satisfied with William's current role as the Prince of Wales.
The survey of 4,000 people also indicated that 49 percent of the British public think Charles is doing a good job as monarch.
Among the least popular royals was Prince Andrew (four percent) and his children Princess Beatrice and Eugenie (both seven percent).
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