Prince William played a significant role King Charles's Coronation at Westminster Abbey on May 6, 2023. As heir to the throne, he was tasked with draping the Stole over his father's shoulders as a symbol of the sacred nature of kingship as well as securing the Imperial Mantle - the robe worn at the moment of crowning. But in a candid clip captured during rehearsals for the Coronation on May 3, 2023, it became clear that William had a far more important role to play. Pomp and ceremony aside, he was simply a son supporting his father on what was the most momentous day of his life. In the BBC documentary Charles III: The Coronation Year, Prince William practises with the clasp on the Imperial Mantle, also known as the Robe Royal or Pallium Regale. 'It's quite a small catch,' William said. 'On the day, it's not going to go in, is it?' 'No,' Charles said as he bursts into laughter. 'You haven't got sausage fingers like mine.' The father-son pair then run through the homage - the touching moment in the ceremony where William pledges his allegiance to the King. Kneeling with his hands between the King's, William recites: 'I, William, Prince of Wales, pledge my loyalty to you, and faith and truth I will bear unto you, as your liege man of life and limb. So help me God.' He is then instructed by Mark Burch, the Precentor of Westminster Abbey, to kiss Charles on the cheek. But before he does so, William breaks the palpable tension in the historic abbey, by tickling his father's face. Now smiling, Charles points out that the kiss should have been planted on his left cheek, rather than his right. 'Wasn't it that side?' Charles asks, pointing at his right cheek. When Rev Burch confirms that it is 'normally the left side', William bends down to kiss his father for the second time, quipping: 'Your left cheek is better.' In an aside to the cameras, Rev Burch said: 'I think the moment of the Prince of Wales kissing his father at the homage, it's a moment that a lot of people saw. 'That really wonderful connection. I mean, priceless.' Also present at the rehearsals was Richard Jackson, the Bishop of Hereford, who observed how close William and Charles are. 'I think what struck me particularly is how extraordinarily affectionate they are,' he said. 'They are clearly a very close family of all the generations. 'In a sense you felt you were part of a family occasion as well as a royal occasion and a national occasion.' During rehearsals, William prioritised making his stoney-faced father laugh rather than fussing around with the regalia. But on the day itself, he stoically carried out his duties. He clasped the Robe Royal around his father's shoulders without a hitch and made sure to kiss Charles on the correct cheek. There is no doubt that throughout the ceremony William would have been keenly aware that the next person to bear the weight of the Imperial State Crown would be him. Relegated to the third row alongside Princess Beatrice and Princess Eugenie was Charles's second son Prince Harry. The King's Coronation marked the first time the Duke of Sussex was pictured with the Royal Family - whom he lambasted in his bombshell memoir Spare - since the funeral of his grandmother the late Queen. Unable to wear military dress to the Coronation as this is a privilege reserved for working members of the family, Harry looked dashing in a sleek three-piece morning suit with an assortment of medals on his chest. After the ceremony, the newly crowned King and Queen were joined on the balcony by an array of familiar faces including Prince William and Kate, as well as the Duke and Duchess of Edinburgh – all of whom are working royals. Prince George, Princess Charlotte and Prince Louis also joined their parents on the balcony, waving enthusiastically to the crowds of adoring fans. But their uncle Prince Harry was nowhere to be seen. Minutes after the Coronation ended, he had jumped into a BMW and been taken to Heathrow where he boarded a flight to Los Angeles. He was in the UK for just over 24 hours. It is believed the duke was eager to get back to his £11million Montecito mansion to celebrate his son Archie's fourth birthday. A well-placed source told the Daily Mail's Royal Editor Rebecca English at the time that the King was 'genuinely quite disappointed' that Harry did not stay. Rebecca later wrote that the King had raised a glass to toast Archie’s birthday at a family lunch after the Coronation – a tribute to the grandson he has barely seen. Insiders close to Prince Harry told People Magazine the ongoing 'strained' relationship with his father five years after the Duke and his wife Meghan Markle quit frontline royal duties and moved to California. Sources close to the Duke have told of his calls and letters to relatives being left unanswered. And he is said to have found out his father the King was recently admitted to hospital on March 27 through media reports rather than being told directly. William, on the other hand, appears to have grown closer to his father amid his cancer battle. While the King underwent treatment, the Prince of Wales stepped up to the plate and took on a long list of royal engagements such as joining leaders from across the world to remember the D-Day fallen. Since being crowned King, it is also believed that Charles has consulted his eldest son on tricky family issues including the likes of Prince Andrew and Megxit. Their joint efforts to tackle these issues is said to have boosted both their personal and working relationship. 'If there was ever a green-eyed monster or a sense of rivalry between the two, that is a chapter of the past,' the friend told The Times. 'The King sees his son as a useful ally on family matters and increasingly in discharging the duties of nation and state.' A source close to William added: 'He very much wants to support his father. That isn’t something new, but of course with everything the King is going through with his treatment, he will continue to support him as much as he can.' Taking to the stage in front of 20,000 people at the Coronation concert held at Windsor Castle in 2023, William's love for Charles was clear. 'As my grandmother said when she was crowned, "Coronations are a declaration of our hopes for the future" and I know she is up there fondly keeping an eye on us and she would be a very proud mother,' he said as the crowd roared. 'At the heart of the pageantry is a simple message: service. My father's first words on entering Westminster Abbey yesterday were a pledge of service. 'It was a pledge to continue to serve because for over 50 years in every corner of the UK, across the Commonwealth and around the world, he has dedicated himself to serve others. 'Pa, we are all so proud of you.