Kate Middleton, 41, and Prince William, 40, are the definition of “opposites attract”, according to a royal author who spoke exclusively to Express.co.uk.

Kate Middleton and Prince William have been married for nearly 12 years and are now parents to three children. Royal author Tom Quinn has written a new book called “Gilded Youth” centred on growing up in the Royal Family. Mr Quinn spoke exclusively to Express.co.uk to explain what the Prince and Princess of Wales are like behind the scenes.

Tom claimed: “We know from the book Spare that William is more inclined to emotional outbursts and sudden rages. That’s a thing that goes back through the generations of royal males, especially heirs to the throne who tend to have tantrums.

“I mean, Harry is the same. It’s interesting that William was drawn to, as you were saying earlier, opposites attract. Everyone I have spoken to said Kate is almost unnaturally calm.”

The expert argued that the Princess of Wales filled a hole in the Prince’s life that was left when his mother sadly died in 1997.

Tom opined: “As we all love Diana, she wasn’t a stable presence for William. I mean, aside from the trauma of her death when he was 15, we’ve got to remember that she was much more cuddly with William and Harry than Charles ever was.

Kate and William have been married for 12 years 

Kate comes from a very stable background according to an expert

“But at the same time, she grew up with nannies and governesses so the boys were left very much with staff while she desperately searched for love. So I think he didn’t bond with his mother as much as perhaps sometimes we think.

“Kate represents that solidity that the late Queen represented, a kind of never complain never explain, just very steady all the time. For someone like William who’s much more emotional and prone to lose it, that’s very attractive because when he loses it, she doesn’t.”

According to Tom who once interviewed the Prince of Wales, William has key personality traits that are the complete opposite of Kate’s.

He explained: “I interviewed William at this polo match, and you could see the irritation, he was about to lose it. Somebody else kept coming up to him and annoying him and pestering him, and he stormed off in the end. Now Kate would never do that.

“But she comes from a family like that. Kate, whether she is consciously emulating the Queen, I don’t think she is, I think she just is a very calm person who learns very quickly.

“She’s learned how to be a royal brilliantly. But because of her personality and her background, you know, her parents didn’t complain, or if they did, it didn’t make a huge fuss.”

Despite William being more “prone to tantrums”, the Prince and Princess deal quite well with palace aides, according to the expert.

Tom added: “William and Kate don’t generally complain about the system in the same way they don’t complain about press coverage.

Prince William suffered trauma of losing mother at age 15

“They don’t complain about the vast number of aides, that just goes with the territory.

“Neither William nor Kate has any rebel in them. There are lots of fuddy-duddy courtiers who don’t want things to change.

“But from what I’ve heard Kate’s very good at charming them and getting her way in without sort of going head to head which again, is why Meghan came unstuck because she always went head to head.”

Tom argues that Princes William and Harry have a few things in common that are rarely noticed.

He suggested: “In many ways, the two brothers are very similar. But they’re also very different.

“They’re both with women who made the decision to run the show. They both have married women who are strong, but they’re strong in different ways.

“It is their attempt to make up for being children with just nannies looking after them. William was very lucky to get Kate because she’s not from that split, uneasy, emotionally distant background. She’s giving him what he’s always needed.

“Kate has had a very structured upbringing, being very close to both her parents and her siblings. Everyone I’ve spoken to about the family says that that was a key part of it, they just made the children feel good about themselves, especially Kate who had this solidity that comes from having a good relationship with parents who don’t divorce.”