Prince William & Kate Middleton Reported Secret to Their Successful Marriage Includes This ‘Naughty’ Side

What is the secret behind Kate Middleton and Prince William’s successful marriage? Well, one royal expert believes it is this unexpected side to their personalities that keeps the Prince and Princess of Wales’ spark alive — and it’s a vast contrast from their very proper public image .

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“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 Life of Charles III , told Fox News Digital. “They’ve certainly cleaned up their act for the children’s sake, but they can still make each other double over laughing.” That tidbit of palace insight gives fans a glimpse of what Kate and William are like behind closed doors — they might be conservative in private, but not necessarily in real life.

Andersen’s revelation aligns with The Telegraph ‘s understanding that Kate is much more relaxed when she’s not in front of royal fans. Her Taylor Swift-esque video in September that gave a cinematic update about her cancer battle was the Princess of Wales’ vision. “This is her,” the outlet said while noting that she prefers to live a more authentic life after going through a tough year.

That’s why the public saw quite a bit of unexpected PDA from Kate and William in the video. They are a little more hands-on than people expected, but not everyone loved the message, including King Charles III. All that lying round, hugging and kissing – they’re not soppy teenagers,” a source told the Daily Mail. “It felt manipulative.” A second insider dared to call the video “distinctly un-regal.”

But why does Kate have to adhere to a stereotypical view of royalty? She should be able to express her thoughts so fans can get a genuine view of her personality. Now, we don’t expect her to be ripping dirty jokes to the media — Kate can leave that for William — but she should feel free to express her more playful side in public.

Giving the Princess of Wales more freedom during her royal appearances gets a thumbs-up from Andersen. “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,” he praised. “With sports, as with everything else, it seems as if she never makes a wrong step.”

Before you go, click here to see more photos of Prince William & Kate Middleton through the years.