As the world looked on, 12-year old Prince Harry, bound by duty and the pressures of royal tradition, walked behind the coffin of his beloved mother, Princess Diana.

Heartbroken royal fans were left speechless at the sight of Diana’s sons making their way through the streets of London on their devastating procession on that dark day in 1997.

Prince Harry would later recall in his tell-all memoir Spare that he felt “numb” during the walk but gained strength from his older brother Prince William, who he kept in his sight despite having his eyes on the ground.

Now, as Prince Harry prepares to mark his milestone, 40th birthday on September 15, friends say he is at a crossroads as he struggles to find his sense of purpose amid the destruction of his brotherly bond and the ever-growing harsh reality of being cut off from the royal family.

A recent Sunday Times profile gave insight into Harry’s personal pain as he enters his fifth decade, saying the exiled royal is torn between battling old demons and forging a new life.

“All he does is spend time looking back,” a former aide told The Sunday Times. “If only he could wrench his neck around and look forward.”

The world has watched Harry’s metamorphosis through the years from fun-loving party prince to earnest eco warrior — albeit one who travels by private jet — determined to right what he views as the wrongs of the past and his royal upbringing.

Harry and William’s once-tight relationship, forged through love and heartache, appears irretrievably broken due to the damage caused by the revelations in Spare, as well as the Oprah Winfrey interview and the Netflix series Harry & Meghan.

The pair are now poles apart and can barely stand to be in the same room, making for an awkward exchange at the recent memorial service for their uncle Sir Robert Fellowes, the husband of Princess Diana’s older sister.

The brothers did not speak to each other at the service, which marked the first time he and William had been in the same room for over a year.

“William and Harry were both there,” a source told The Sun. “But we never saw them speak to each other and they were keeping their distance.”

Following the painful encounter, Harry quickly returned to his mansion in California’s A-list haven Montecito where, according to friends quoted by The Sunday Times, he is becoming more dissatisfied with his life in “gilded exile”.

According to People magazine, Harry is the one who is desperately trying to heal the rift, sending his older brother a barrage of ignored texts and emails.

A friend of Prince Harry’s told The Sunday Times: “Harry simply cannot do without his brother.”

William, however, is moving on and appears to have closed the door permanently on Harry after his attacks on Princess Catherine in which he accused the UK’s most popular royal of sparking the long-running feud with Meghan Markle with her alleged “cold” behaviour.

Meanwhile, King Charles is increasingly frustrated over his son’s seemingly endless fight over his security in the UK.

The monarch, who spent just minutes with his youngest son during Harry’s mercy dash from California after his cancer diagnosis, has ordered Harry, according to royal expert Tom Quinn, to stop “publicly complaining”.

In the background, Harry and Meghan’s much-derided Brand Sussex continues to take hit after hit.

The pair’s recent “quasi royal” tours of Nigeria and Colombia, during which they received stately welcomes and spruiked their charitable causes, was viewed by some as a desperate attempt to stay relevant to an increasingly disinterested public.

Meghan’s much-hyped lifestyle brand, American Riviera Orchard, has failed to sell a single product months after its lavish launch on Instagram.

Insiders have told US Weekly that Meghan plans to release her line of pricey jams and homeware products next year to coincide with her new Netflix series, which will delve into the tricks she has learned as “a modern-day hostess”.

Harry has announced he is working with his employer BetterUp to create a life-coaching university, a move that has raised questions about whether the royal is qualified to take on such a role.

Following his 40th birthday celebrations, the royal will head to New York, where he will take part in various summits and meetings during Climate Week.

Speculation that William might attend the Earthshot Prize, meaning he could be in the city at the same time as his brother, was quashed after it was revealed the future king would be staying in the UK.

Prince Harry is unlikely to receive any birthday wishes from his brother and his celebrations, it would appear, will be short-lived as he plots his next move and works out where exactly he will go from here.

See more of Prince Harry’s life below in pictures.