"She and William are very experienced parents and I'm sure they love all three kids equally - but probably in different ways."

The expert then continued, "George because he's the first-born and has a destiny to fulfil, Charlotte because she's the only girl, and Louis because he's the youngest."

Ms Bond then discussed Charlotte and George's role in their younger brother's life, adding: "Charlotte seems to keep a watchful eye on her little brother and make sure he's behaving.

"She's not always successful. But Louis has won the hearts of many people with his antics, and I'd much rather see a cheeky chappie than an immaculately behaved kid."

While Princess Kate has not spoken about her feelings ahead of Louis’ birthday tomorrow, she did mention a few years ago that her youngest son seems to be growing quickly.

At a royal engagement at a maternity unit in Surrey years ago, Kate told some mothers: "I keep thinking Louis is a baby, but he’s a big boy now."

How the young royal will celebrate his birthday remains unknown, but it is likely he will celebrate with his parents and siblings.