Since his birth on June 21, 1982 to father Prince Charles and mother Princess Diana, Prince William has been a public figure.

But what kind of person is Prince William in his private life as he approaches the milestone of turning 40 this week?

According to the Mirror, he is a man with a "wicked sense of humor" and a "cool determination, quick wit, and a compassionate edge." The paper also reports that he is at peace with his future as king and, according to friends, he has what it takes to handle the top job. (One example of William's constantly burgeoning leadership is his dragging his feet this week against his uncle Prince Andrew attending the Order of the Garter ceremony, which he was expected to attend.)

The Duke of Cambridge, second in line to the throne, "has always been more reserved than his brother [Prince Harry]," the magazine reported. But his sense of duty keeps him going and keeps him motivated for his future as king, his long-term mentor, Jamie Lowther-Pinkerton, told the Daily Mail.

"He hasn't been happy to sit on his hands [about what's about to happen], but has looked at it obediently," said Lowther-Pinkerton.

Sources told the Mirror that while William was once furious about his future, he is now more at peace with himself than ever before.

However, the magazine reported, "William was not always neat and proper. When he was growing up, his friends told him, 'He enjoyed himself a great deal ...... ' Unlike Harry, though, he never got caught! '"

He married his college sweetheart Kate Middleton in 2011, and his sense of humor was on full display when the newlyweds toured the South Pacific in 2012.

"The royal couple stayed in a house on one side of a large bay, with the support team staying on the other side," a source told The Mirror. Late one night, after a particularly grueling day, the Cambridges' team decided to go for a dip in the warm water. Then, out of nowhere, an aide (name withheld) was dragged into the water coughing. Everyone panicked, thinking he had been attacked by a shark, and all hell broke loose. But it was William."

The prince, sources say, "sniffed out their nightly dip." To play a prank, he swam around the bay, quite underwater, as he is an expert diver!"

The father of three is also "an incredibly empathetic boss" and "treats his subordinates really well, even sending get well wishes to those who are out sick," sources say.

"He loves to chat when their dates go bad," the source says.

According to the Mirror, the future king has told friends, sources, and royal family insiders that he is confident he has what it takes to be king and "does a good job at it."

"The coming decades will be the most difficult we have ever experienced as a nation in modern history," says one close friend. And William is ready to step up to the plate."