The Prince Harry stare that said: I've become a Spare part

It was the stare that spoke a thousand words about the broken bond between two once close royal brothers. Diana, Princess of Wales, had insisted they be brought up as equals. But as he was relegated to a third-row seat, The Princess Royal's hat obscuring his view, there was no mistaking the Duke of Sussex's sense of unease as he briefly glanced across to the Prince of Wales during their father's Coronation on Saturday.

Marking the first time Prince Harry has been in the same room as the King and the heir to the throne since the publication of his bombshell autobiography Spare, which was highly critical of the Royal family, it was never going to be an easy reunion. Yet in seemingly not exchanging a single word with his father or brother during his whistle-stop visit, returning to California after just 36 hours, the father of two, 38, could not have looked further removed from the Firm he once called home. His sidelining appeared all the more stark in comparison to the prominent role Prince William, 40, played in publicly pledging to be the King's "liege man of life and limb".

The 74-year-old monarch looked visibly moved after his eldest son leaned in to kiss him on the cheek, responding with a heartfelt: "Thank you, William."

The sorrow in his eyes appeared to speak to a sense of regret that while he has gained a stalwart and supportive heir - he has lost his "spare". At the end of the Duke and Duchess of Sussexes' tour of Africa in 2019, Prince Harry spoke of being on a "different path" to Prince William. "Part of this role and part of this job and this family being under the pressure it's under, inevitably stuff happens," he said.

"We're brothers, we'll always be brothers. We're certainly on different paths at the moment but I will always be there for him and as I know, he'll always be there for me. "I love him dearly."

Four years on, however, and following the couple's Oprah Winfrey interview, six-part Netflix documentary and tell-all memoir, the brothers don't just seem to be on different paths but different planets. Royal insiders admit there is little hope of reconciliation with Prince William said to be "absolutely horrified" by what Prince Harry wrote about him in Spare. The Duke has called for an apology but as a source close to the Prince explained: "There has been no acknowledgement, let alone apology from the Sussexes for the hurt they've caused."

Ironically, Prince Harry's actions have only served to make him even more insignificant in the royal pecking order, him having constantly complained of having to play second fiddle to his brother.

Although he will always retain his fifth place in the line of succession (despite being stripped of his His Royal Highness style), his decision to step down from public duties has only served to further elevate the Prince and Princess of Wales. Appearing every inch a future King and Queen on Saturday, the couple and their children Prince George, nine, Princess Charlotte, eight, and Prince Louis, five, have been front and centre of this weekend's celebrations reaffirming their superior status in the House of Windsor.  With a global audience of billions watching the two-hour ceremony unfold in Westminster Abbey - the coverage rather puts the Sussexes' Netflix viewing figures into perspective.

It is no coincidence that it was Prince William and his wife, 41, who were chosen to be the warm-up act at the Dog and Duck in Soho on Thursday, before once again popping up for a walkabout in Windsor on Sunday ahead of the Coronation Concert. They are also expected to make an appearance at Monday's "Big Help Out" having stepped up as King Charles and Queen Camilla's supporters in chief.

And as with Queen Elizabeth II in the later stages of her reign, the couple can only expect to take on more responsibility as the Caroleon era continues. At 74 and 75 respectively, the King and Queen are not going to be able to undertake lengthy overseas tours to far-flung destinations and, as time goes on, will become increasingly reliant on the younger generation.

The burden on the Prince and Princess of Wales is even greater in the absence of the Duke and Duchess of Sussex and the Duke of York - but on the plus side, it means the couple can command much more attention and many more column inches for the causes closest to their hearts.  Prince William's speech at the Coronation concert is proof of their desire to connect with as many people as possible on the subjects they hold most dear. At this stage, Prince Harry and Meghan could only dream of such projection.

The truth that stared us all in the face as the King and Queen were crowned on Saturday is that Prince Harry is now a spare part in an institution that can survive without the Sussexes - but whose future depends on the Prince and Princess of Wales.