Gilded Youth” author told Express.co.uk recently that the Duke of Cambridge is “prone to tantrums,” so says a Kensington Palace source close to Quinn.He added that the royal family’s golden couple often have “rows” and their marriage is “not perfect.”During these wild fights, William and Kate are known to “throw cushions at each other,” but their arguments are otherwise “always kept under control.”William and his wife’s relationship appears perfectly content from the public’s perspective, and the pair’s marital bliss can be boiled down to the late Queen Elizabeth‘s “never complain, never explain” motto, Quinn said.“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 said.The expert continued, “They very rarely complain and when they do it’s always in measured terms.”The Post has reached out to Kensington Palace for comment. Last month, William was caught gushing over Middleton in a sweet moment during a visit to Birmingham, England.While couple met with onlookers at the Rectory restaurant, where the Duke of Cambridge raved about his longtime lady.