These days Prince William exudes an aura of confidence as he makes official appearances and shakes hands with celebrities and members of the public. He appears relaxed, often cracking jokes and putting people at ease.

But that wasn't always the case, according to body language expert Darren Stanton. As a child, the current Duke of Cambridge was actually quite shy and used assertive gestures to defend himself.

William, who turns 40 on June 21, reflects on the confidence the royal family has found over the years and the major role his wife, Kate Middleton, has played in its evolution, according to Stanton.

"Both William and Harry were quite introverted as children and didn't seem that confident," Stanton told Marie Claire on behalf of Betfair Slot (opens in new tab).

"In earlier pictures of William in public, he exhibits self-affirming behavior and appears a little less confident.

"William has been seen in a certain posture, made famous by his brother Prince Harry, in which he places his palms inside his jacket.

"It is a very reassuring gesture when one is feeling anxious or worried, and William has shown this on occasion. William sometimes plays with the buttons on his jacket or touches his cufflinks.

Over the years, however, the Duke has gained confidence.

"Over the last few years, William has really grown as a senior royal, as an empathizer and communicator. Part of that is due to his marriage to Kate Middleton," Stanton explains. [Kate] has been instrumental in boosting William's confidence, especially at royal functions and in his meetings with other civilian dignitaries. Of course, fatherhood has given William a great deal of peace and tranquility, and has boosted his confidence in himself."

Stanton added, "These days, you don't see much of the jacket gesture, and it's rare to see him playing with his cufflinks." This suggests that William has grown in his own skin and has become very comfortable in the role of future king.

Importantly, the Duke no longer displays the "stiff upper lip" that was seen in the past and early years of his marriage.

"His willingness to express affection in public with Kate and his happiness when doing so has become more prevalent in recent years," says Stanton.

"Attending premieres such as the James Bond premiere and the recent premiere of Top Gun with Tom Cruise, William has kissed Kate quite openly and held her hand."

"In their interactions, the couple have been seen intimately laying their hands on each other or just sitting and holding hands. This indicates that the couple is very much in love and that Kate is a central part of William's life."