What’s the secret behind Prince William and Kate Middleton’s 13-year marriage? Despite being in the public eye and gearing up to be the future king and queen consort, experts told Fox News Digital that their playful side is the glue that keeps them together – and it’s something they’re passing on to their three children.

“William once described Kate’s sense of humor as ‘naughty’ and his own as ‘dirty,’ and claimed that it was one of the most important things that drew them together,” said Christopher Andersen, author of “The King.” “They’ve certainly cleaned up their act for the children’s sake, but they can still make each other double over laughing.”

“William and Kate have also passed their wacky, slapstick, Monty Python-meets-Benny Hill sense of humor on to the children,” Andersen shared. “And like all parents of young children, William and Kate find themselves refereeing when the kids fight over the TV remote, or when the inevitable teasing that goes on between siblings turns into the equally inevitable wrestling match.”

The Prince and Princess of Wales married in 2011. They share three children: Prince George, Princess Charlotte and Prince Louis. (Samir Hussein/WireImage/Getty Images)

Andersen’s statements came shortly after Kate’s brother, James Middleton, spoke out on the “Walking the Dog” podcast. He revealed that William, 42, used to make up excuses to get out of the Middleton family game nights because he found them too competitive.

“Competition runs in the royal blood,” Andersen pointed out. “No one enjoyed a spirited contest more than the late Queen Elizabeth II, whether she was cheering on her horse at Ascot or watching a tug of war at the Highland Games. Prince Philip was a world champion four-in-hand carriage driver and Princess Anne competed in equestrian events at the Olympics. And King Charles was such a passionate polo player he suffered countless injuries in the process.”

James Middleton and Pippa Middleton, Kate Middleton’s siblings. (Andrew Milligan – WPA Pool/Getty Images)

“But the royals look like pikers compared to the Middletons, who taught Kate that winning was pretty much everything,” said Andersen. “William and Kate’s card games are so heated and all-consuming that William makes excuses to avoid being sucked in. But away from his win-at-all-costs Middleton in-laws, William has never shied away from going up against Kate in a contest.”

“William once described Kate’s sense of humor as ‘naughty’ and his own as ‘dirty,’ and claimed that it was one of the most important things that drew them together.”

— Christopher Andersen, author of “The King”

The Prince and Princess of Wales on a skiing trip on March 3, 2016, in the French Alps, France. (John Stillwell – WPA Pool/Getty Images)

“The Prince and Princess of Wales have always been competitive about pretty much everything – foot races, swimming races, board games, card games, you name it,” he shared. “Now this trait has been passed on to George, Charlotte and Louis – all of whom have been taught to give it their all. Unfortunately, this often leads to heated arguments about cheating and breaking the rules – which in turn leads to the occasional game board being tossed and pieces sent flying.”

Prince William jokes around with Kate Middleton while at the Virgin Money London Marathon in 2017. (Mark Cuthbert/UK Press via Getty Images)

There is one family leader, Andersen noted. And it’s not the Prince or Princess of Wales.

“Big sister Charlotte is the ‘Louis-whisperer’ in the family,” he revealed. “She is best equipped to get her rambunctious little brother to behave when – as the youngest child in the family often does – Louis goes off the rails to get attention.”

In September, Kate Middleton announced she was “cancer free” after completing chemotherapy treatments. (Will Warr)

“But since Kate’s cancer diagnosis, the children have been more sensitive to their mother’s needs for a little more peace and quiet than usual,” said Andersen. “But their overall family dynamic – the hectic schedule of school, after-class activities, birthday parties, and play dates that fill the calendar – hasn’t changed. That continuing sense of normalcy has without doubt been key to Kate’s recovery.”

Christopher Andersen, author of “The King,” shared that Kate Middleton comes from a competitive family. (Suzanne Plunkett/Pool/AFP via Getty Images)

British royals expert Hilary Fordwich told Fox News Digital that, unlike William, Kate, 42, grew up in “the most normal background,” which is something she has incorporated into her royal household.

“She was always used to chores,” said Fordwich. “Her parents were busy building their Party Pieces business that her mother Carole Middleton founded. Young Kate was instrumental in developing party supplies specifically for babies and young children, so she knows the power of active, engaged children who learn responsibilities. Prince George is currently assigned to clean out their pet guinea pig’s cage.”

Prince William and Kate Middleton are known for their competitive streak, which plays an active role in their marriage. (Alastair Grant/Pool/AFP via Getty Images)

Royal expert Richard Fitzwilliams told Fox News Digital that William has been eager to also give his children a sense of normalcy behind palace doors.

“After his marriage to Catherine… William has done his utmost to make his life and that of his family as normal as possible,” he said. “Their mutual love of sports has been passed to their children.”

Prince William throws a football as he attends an NFL Foundation flag football event in London on Oct 15, 2024. (Kim Cheung/AP Pool/AFP via Getty Images)

“It was a feature of royal tours to see them compete in archery, cricket, or sailing,” he shared. “This was unusual, but people identified with it, and it added a competitive flavor to normally predictable schedules.”

Catherine, Princess of Wales speaks to members of the emergency services during a visit to Southport Community Centre in northwest England on Oct. 10, 2024. (Danny Lawson/Pool/AFP via Getty Images)

Since announcing she was cancer free in September, Kate has returned to private meetings at Windsor Castle and public royal engagements. British broadcaster and photographer Helena Chard told Fox News Digital that the Prince and Princess and Wales have remained dedicated to being hands-on parents – and introducing their passions to their little ones.

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“Princess Catherine and Prince William love sport and the great outdoors,” said Chard. “They also love team spirit and have passed on their passions to their children. They have always been an incredibly down-to-earth and caring family. Now, I sense a new lease of life in them all since Princess Catherine’s cancer scare. They have an even greater energy, which you can feel in their company.”

“Last weekend Princess Catherine cheered on Prince Louis at his football match,” Chard shared. “[That] thrilled the other mums who she chatted with freely. The mums enjoyed her charming, gentle superpower, which is also the strength behind her husband. I enjoy seeing Princess Charlotte’s care, empathy and love toward her brothers at events… I see the Wales family becoming more and more the people’s family.”

An animated Pippa Middleton, Princess Charlotte and the Princess of Wales watch the men’s final match at Wimbledon. (Karwai Tang/WireImage/Getty Images)

“It is heartwarming that they are the future of our royal family,” Chard added.

Andersen previously told Fox News Digital that it’s Kate’s “sporty” personality that instantly drew William in. The couple married in 2011.

“Kate has always been described as ‘sporty,’” said Andersen. “It’s one of the main things that attracted William to her. It also made her an easy fit for the hyper-athletic royal family. Kate may be the sportiest royal of all. In high school, she was a star player in hockey and tennis. She’s also an accomplished skier, runner and sailor.

Prince William and Kate Middleton gear up to play goalball, a visually impaired Paralympic sport, at Bisham Abbey National Sports Centre near Marlow, west of London, on Oct. 12, 2023. (Suzanne Plunkett/Pool/AFP via Getty Images)

“Kate has always seemed game for anything. What sets her apart from the rest of the royal pack is that she always does it with a smile… With sports, as with everything else, it seems as if she never makes a wrong step.”