Prince William and Kate Middleton's marriage has its ups and downs just like that of every other couple, according to a royal author.

Royal expert Tom Quinn made the claim in his new book, "Gilded Youth: An Intimate History of Growing Up in the Royal Family," in which he discusses the traditional upbringing of the British royal family and cites testimony from palace staff, historical sources and royal insiders.

"Someone at the palace told me about the nicknames they have for each other," Quinn told Fox News Digital of the Prince and Princess of Wales. "But it's not all sweetness. They have terrible rows where they throw things at each other. Kate might seem to be a very calm person, and William also. But it's not always true. Because the big stress for William and Kate is that they're constantly surrounded by [palace aides]. It's like a Jane Austen novel."

International Business Times could not independently verify his claims.

An unnamed former palace staffer who knew Middleton reportedly told Quinn that the future queen consort calls her husband "babe."

Meanwhile, Prince William reportedly calls Middleton "Babykins" and "Duchess of Doolittle" or "DoD," a gentle dig at his wife, who was allegedly criticized by the late Queen Elizabeth II for not having a full-time career before the couple tied the knot in 2011.

Quinn also learned from palace sources that Prince William fusses over his wife's "endless mane of hair," prompting her to joke about his baldness and call him "baldy," according to the royal author.

But although they argue, Quinn said the pair also quickly "cozy up."

Between the two, the author said that Middleton is the calmer and more level-headed one.

"Kate is very much the calm one," Quinn claimed. "William is the one who's a bit hotheaded. We see an example of that in Harry's book... But Kate is very level-headed. She's the one who will pour oil on troubled waters and go, 'Let's not stir things up.'"

"Of course, privately, William and Kate, like all couples, fall out, row, shout at each other and say unkind things to each other, but Kate is an appeaser by instinct and William always gives way as he had more than enough emotional turmoil, divorce and disruption as a child," Quinn alleged. "He hates confrontation."

During their 2010 engagement interview, Prince William shared that their sense of humor makes him and Middleton compatible.

"She's got a really naughty sense of humor which really helps me because I've got a really dirty sense of humor, so it was good fun, we had a really good laugh, and then things happened," he said at the time.

The Prince and Princess of Wales tied the knot on April 29, 2011. They have since welcomed three kids — Prince George, 9, Princess Charlotte, 7, and Prince Louis, 4.