Prince William turns 40: Birthday photos show duke's priorities

The Duke of Cambridge celebrates his 40th birthday on Tuesday and will spend it privately with his family, according to Kensington Palace.

It has issued three new photographs of Prince William to mark the occasion - but if you were expecting official, formal royal portraits, then think again.

The three previously unseen images were taken a couple of weeks ago, when Prince William was out selling The Big Issue in London. They tell us something of where the duke's priorities lie on this landmark birthday.

He has deliberately avoided the traditional royal photo and gone for something that portrays him "at work" on an issue that his staff say is very close to his heart.

As he heads into his 40s, homelessness will increasingly become a focus for him and he has history in this area.

Back in 2009, he slept out on the streets of London with the Chief Executive of Centrepoint, Seyi Obakin, to help understand the experience of homelessness. Thirteen years on, he is still actively involved in finding solutions to the problem

"He's definitely part of that story for us but more importantly we are part of the story for him," says Seyi Obakin. "He is not just interested, he is committed to the cause of helping to end youth homelessness."

As Prince William fine-tunes the kind of public work he does, he's also making big decisions with the Duchess of Cambridge about his private, family life.

Prince William's marriage to Kate has provided stability and support during some difficult times. Fatherhood also seems to suit him. Their three children put in a star turn during the Platinum Jubilee weekend - although expect future appearances from them to be carefully timed and managed.

This summer the Cambridges will leave their home at Kensington Palace for a new life in Windsor. It is a decision that has been driven by personal reasons.

Behind the castle walls, they will have more freedom than they currently have in London. Prince George, Princess Charlotte and Prince Louis will go to a private school nearby. It also puts William closer to his grandmother, the Queen, at a time when she is stepping back and he is stepping up.

One issue that remains unsettled and unresolved on his 40th birthday is Prince William's relationship with his brother, Prince Harry. There was no public reconciliation during the Jubilee weekend or even the slightest sign that they are on better terms.

"William is still very hurt about some of the things that his brother and his sister-in-law have said and done," says Katie Nicholl, author of The New Royals. "He does ultimately want there to be a rapprochement but there are quite a few bridges to be rebuilt before they get to that stage."

There have been times in the past when William was labelled a "reluctant royal" and perhaps seemed burdened by the role that lay ahead for him. Something seems to have shifted.

The once cautious, contained prince is increasingly looking like a more open, confident future king. Publicly, he seems to have found the causes that interest him and where he feels he can make a difference.

Don't expect to see him take on take on new patronages and charity work in the years ahead. He will instead try to make a greater impact in the areas he's already invested in - homelessness, the environment and mental health.

Prince William knows that the years ahead will be filled with significant change. But for now, at 40, he seems settled in both his public role and his private life.