While the future King and his wife were thought to be spending his birthday on Thursday privately at Highgrove, his father's Gloucestershire estate, there was speculation over what he plans to do with the money – and more pressingly his career.
Under the terms of Princess Diana's will the bulk of her estate was held in trust for William and his brother Harry to be handed over when they reached 25.
After her death, executors changed the inheritance age to 30.
CLICK ON PHOTOS FOR A SPECIAL REPORT ON WILLIAM'S LIFE IN THE SPOTLIGHT
Royal aides moved to quash rumours that he and the Duchess of Cambridge plan to buy a large country pile – an understandable decision given this transitional time in William's life.
Before the year is up, he must decide whether or not to continue with his career in the RAF.
A difficult choice given his passion for his job, the issue has been further complicated by the health of his beloved grandfather, Prince Philip.
The Duke's recent hospital stays have only highlighted the fact that soon the younger generation will have to step into the spotlight.
And William is now said to be "very seriously" weighing up his options.
It's thought his initial instinct is to take on all, or part of, a new 36-month tour of duty.
As one confidant told the Daily Mail: "It's a core part of who he is.
"The confidence and contentment he has gained from his career has seeped into every aspect of his life."
"I honestly believe it is no exaggeration to say that his career satisfaction was in a large way responsible for his decision to finally pop the question to Kate," another added.
"All of a sudden, the pieces of the jigsaw finally slotted together."
In the cockpit of his helicopter, William is given the chance to enjoy a 'normal' life – many of those he has helped rescue have no idea they were saved by the future King.
And being based in Anglesey, where he and his wife share a home, also gives him relative anonymity.
However, should he extend his time in the air force, the couple will almost certainly have to transfer to a new base – quite in another remote area such as northern Scotland.
The Prince will have to decide whether he and Kate will want to start again so far away from their relatives – particularly if they do have a baby.
On the subject of children, friends have said it's unlikely that the royal couple will trying for a family before their Diamond Jubilee tour of Malaysia, Singapore, Tuvalu and the Solomon Islands in September.
The busy ten-day visit would prove particularly tiring for the Duchess should she be in the early stages of pregnancy.
All of William's decisions are taken with a great deal of consideration for Kate, of whom he is incredibly proud for finding her feet in the royal family.
Sources close to the pilot Prince have revealed that both his grandmother and Prince Charles have resisted putting pressure on him, insisting he must do what’s best for him and the Duchess.
"It is true that the Queen and the Prince of Wales are both incredibly supportive of his career and whatever decision he makes," a friend told the Mail.
"They have made it clear that it is a decision he and his wife have got to take together."
But the second in line to the throne is first to admit that "the other pressure of my life are building".
In the meantime, William will continue to juggle his RAF job with his royal duties.
And the majority of his engagements will be conducted with his wife – a clear indicator they "very much see themselves as a team".