The future king of England, Prince William, will celebrate his 40th birthday over the English summer in an extravagant bash at Windsor Castle surrounded by hundreds of family and friends.

Only two people who matter will miss the party – his mother, Diana, Princess of Wales, who was killed in a car accident in 1997 when William was just 15 years old, and his estranged and only sibling Prince Harry, now living in California.

We’ve watched him grow from a tow-headed schoolboy, to bravely walking behind his mother’s coffin, to a dashing air-sea rescue pilot and a balding father of three.

His life story so far has been told through iconic images and moments.

As he turns 40 on June 21 (UK time), it will be the next decades when he will make the biggest changes, as he assumes an increasingly central role in the royal family to prepare for his eventual accession to the throne.

Prince William at the end of the Platinum Jubilee party outside Buckingham Palace on June 4. Photo: Getty

Two weeks ago, William took centre stage at the extravaganza concert marking Queen Elizabeth II’s 70 years on the throne, lauding his grandmother as an environmental trailblazer as he delivered a call to action on climate change.

“Tonight has been full of such optimism and joy – and there is hope,” he said, as images of wildlife, oceans and jungles were projected on the walls of Buckingham Palace behind him.

“Together, if we harness the very best of humankind, and restore our planet, we will protect it for our children, for our grandchildren and for future generations to come.”

His charities and causes – from mental health to the environment – have given hints of what sort of monarch he might be.

It’s really just the start of a long, distinguished list of passion projects.

Recently, he went undercover to sell copies of The Big Issue, a publication put out by marginalised people who are working to overcome homelessness.

He then visited The Passage, a charity that provides services to prevent and end homelessness.

Both causes were dear to Diana, so get ready to see more of this as William puts his stamp on the new generation of the monarchy.

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‘He will treat things differently’

Slowed by age and health problems, the 96-year-old Queen is gradually handing over more responsibilities to her son and heir, Prince Charles.

Royal expert Professor Pauline Maclaran, author of Royal Fever: The British Monarchy in Consumer Culture, says Prince William has been “very keen to show how he will treat things differently”.

“And so we see that more and more, where the future of the line is being emphasised, with Charles being put more in a kind of holding position for William,” Profesor Maclaran said.

“We’re always reminded that William is after Charles.”

William’s position as the eventual heir to the throne was, of course, sealed at his birth on June 21, 1982, as the first son of Charles and the late Princess Diana.

The world has watched him from the second Charles and Diana presented him to TV cameras outside St Mary’s Hospital in London, through his school days, his courtship of Kate Middleton at the University of St Andrews in Scotland, and their spectacular marriage at Westminster Abbey.

He graduated from the Royal Military Academy Sandhurst, then went on to active duty in the Army, Navy and Royal Air Force then a civilian air ambulance pilot, before moving into full-time royal duties five years ago.

We saw the high and lows, from the heartbreaking tragedy of farewelling his mother through the streets of London, to the happiness of bringing three beautiful children into the world.

Then there was the rift with his brother Harry after his marriage to US soap actor Meghan Markle, and their now-infamous bombshell interview with Oprah Winfrey (and more recently with co-anchor of the NBC News morning show Today Hoda Kotb).

Cue music.

Let’s take a look at his life … so far.

Diana, Princess of Wales holds her son Prince William at Buckingham Palace after the prince’s christening in 1982. Photo: Getty

Happier days. Diana with her baby Prince William at home in Kensington Palace. Photo: Getty

Prince William and his pony with Diana in 1986 at Highgrove House. Photo: Getty

William and Harry in the gardens of Highgrove House in 1986, wearing the uniforms of the 1st Battalion of the Parachute Regiment. Photo: Getty

William and Harry on the chair lift during a skiing holiday in Lech, Austria in April 1991. Photo: Getty

Queen Elizabeth II, Prince Philip, Prince Charles, Diana Princess of Wales, Prince William and Prince Harry stand on the balcony of Buckingham Palace for Trooping The Colour in 1988. Photo: Getty

Diana, William And Harry visit Thorpe Park amusement park in 1993. Photo: Getty

William and Harry on the deck of the yacht Britannia in Toronto, when they joined their parents on an official visit to Canada in October 1991. Photo: Getty

William, Princess Diana and Harry, at the Heads of State VE Remembrance Service in Hyde Park on May 7, 1995 in London. Photo: Getty

William on his first day at Eton. Photo: Getty

Prince William and his family followed Princess Diana’s casket on foot past hundreds of thousands of mourners during her funeral procession to Westminster Abbey in London in 1997. Photo: Getty

Prince William behind the coffin of the Princess of Wales draped in the Royal Standard, on its way to the funeral ceremony in 1997. Photo: Getty

Prince William, in a Union Jack vest emblazoned with the words ‘Groovy Baby,’ at Eton College to commemorate his 18th birthday in June 2000. Photo: Getty

Graduation day, 2005. Photo: Getty

Prince William joined Jon Bon Jovi and Taylor Swift for an impromptu singalong during a gala event in 2013. Photo: Getty

Prince Harry and Prince William. Photo: Getty

Prince William and Kate Middleton faced the media at St James’s Palace, London, after announcing their engagement in 2010. Photo: Getty

The Duke and Duchess of Cambridge in Katoomba, NSW, in April 2014. Photo: Getty

Catherine, Duchess of Cambridge and Prince William, Duke of Cambridge on the balcony at Buckingham Palace with bridesmaids following their wedding at Westminster Abbey on April 29, 2011. Photo: Getty

William, Kate and the family is now complete. Photo: Instagram

Charlotte and George with Kate and William. Photo: Getty

William and Harry at the 2017 premiere of Star Wars: The Last Jedi in London in 2017. Photo: Getty

Ringo Starr is knighted by Prince William at Buckingham Palace in 2018. Photo: AAP

William was the first royal to make an official visit to Israel in 2018. Photo: Getty

Princes Harry and William were in sync en route to St George’s Chapel for the royal wedding on May 19, 2018. Photo: Getty

Prince William trumped wife Kate in hat-boasting honours at Trooping the Colour in 2017. Photo: Getty

A sombre day on many levels at the Commonwealth Day Service in 2020: Photo: Getty

At the beginning of the pandemic in March 2020. Photo: Getty

Prince William and Sir David Attenborough share the stage at the Davos forum in September 2021. Photo: Getty

The duchess, in a sparkly gold gown, and Prince William in a tuxedo stunned as royals at the premiere of James Bond movie No Time To Die. Photo: Getty

William and Kate touched down in Belize, where the transition to a republic is being considered, in March. Photo: Getty

The events just before and during the celebrations of the Queen’s Platinum Jubilee started to give a clearer indication of William’s vision of the future.

William and Kate represented the Queen in March when they made an eight-day tour of Belize, Jamaica and the Bahamas, three of the 14 independent countries where the British monarch still serves as head of state.

They were met with brass bands and gala dinners, but also demonstrations by protesters demanding reparations for Britain’s role in the enslavement of millions of Africans.

Jamaican Prime Minister Andrew Holness told the royals his country intended to become a republic, severing ties to the monarchy.

After the trip, the young royals were criticised as “tone deaf” for perpetuating images of Britain’s colonial rule.

But rather than falling back on the House of Windsor’s traditional response of “never complain, never explain”, William took the unusual step of issuing a statement reflecting on all that had happened.

“I know that this tour has brought into even sharper focus questions about the past and the future,” William said. “In Belize, Jamaica and the Bahamas, that future is for the people to decide upon.

“Catherine and I are committed to service,” he continued. “For us, that’s not telling people what to do. It is about serving and supporting them in whatever way they think best.”

Happy birthday to us! Prince William and Kate will celebrate joint 40th birthdays at one of the Queen’s estates over the UK summer. Photo: Getty

To celebrate Father’s Day in June this year, a photo was released of William and his three children in Jordan in 2021. Photo: AP

Professor Maclaran says the willingness to be approachable is critical for the House of Windsor as it seeks to remain relevant to younger people and cement its role in British society.

“It’s important that William shows there are going to be changes to the monarchy,” she said.

“Otherwise, you know, I suspect it really can’t survive.”