According to reports, the Prince and Princess of Wales’ well-publicized marriage thrives because of a “naughty” secret ingredient. The royal power couple is the proud parents of three adorable children. They exchanged vows in the splendor of Westminster Abbey back in April 2011.

Away from the spotlight, William and Catherine’s relationship seems refreshingly grounded, even though everyone is watching them when they appear in public. According to an expert, the couple’s secret charm is their playful nature, which they are also teaching their kids.

In an interview with Fox News Digital, author Christopher Andersen revealed: “William once called Kate’s sense of humor ‘naughty’ and his own ‘dirty,’ saying that it was one of the most significant things that brought them together. They can still make each other laugh uncontrollably, even though they have definitely cleaned up their act for the benefit of the kids.”

William and Catherine are always seen laughing together at royal functions, and their children—especially the lively Louis—clearly carry on the family’s fun-loving tendencies.

In their official engagement interview in late 2010, Prince William first discussed Catherine’s lighthearted humor. “We obviously met at university – at St Andrews we were friends for over a year first and it just sort of blossomed from then on. We just spent more time with each other, had a good giggle, had lots of fun and realised we shared the same interests and had a really good time.”

He added: “She’s got a really naughty sense of humor, which kind of helps me because I’ve got a really dry sense of humour, so it was good fun, we had a really good laugh and things happened.”

It’s clear that the couple still has that same spark even though they are now proud parents to three kids. Anderson claims that the Waleses have a “wacky, slapstick, Monty Python-meets-Benny Hill sense of humor.”

Their children, Prince George, Princess Charlotte, and Prince Louis, have inherited this sense of humour.

Whether he’s dancing, acting like a jet pilot, making goofy faces, or sticking his fingers in his ears, Louis in particular is known for taking center stage at public gatherings with his hilarious antics. His parents even wrote a thank-you note after the late Queen’s Platinum Jubilee celebrations, mentioning their cheeky youngest.

“Thank you to everyone who turned out to show their gratitude to The Queen and her inspiring 70 years of leadership. From the crowds on the Mall to communities hosting street parties up and down the country, we hope you had a weekend to remember,” they penned. “We all had an incredible time, especially Louis..“