All eyes were on Prince Harry when he arrived at the Coronation - with many people intrigued to see how he would react with other members of the Royal Family.
Despite the bad blood between the Duke of Sussex and the other royals, everyone put aside their differences for Charles' big day.
There were rumours that many of Harry's family members did not wish to speak to him, but he was seen happily chatting to lots of them inside Westminster Abbey.
With wife Meghan Markle staying at home in California with Prince Archie and Princess Lilibet, Harry arrived at the Abbey with Princesses Eugenie and Beatrice and their husbands, Jack Brooksbank and Edoardo Alessandro Mapelli Mozzi.
He was sat beside Eugenie's hubby Jack and Princess Alexandra, the cousin of the late Queen, during the ceremony and dashed off immediately afterwards to get back home to the States.
As well as chatting to some of the royals, there were some awkward gestures and moments with others.
Prince William
There were no direct interactions between Harry and William, with organisers making sure they did not confront one another.
The Duke of Sussex was sat in the third row so he was nowhere near the Prince and Princess of Wales.
But there was one moment when Harry reacted when he got a first glimpse of William at the start of the ceremony.
As William and Kate proceeded to their seats, Harry caught sight of his brother and performed an "ignore" gesture, according to body language expert Judi James.
She told the Mirror: "Harry performed what looked like an oddly-times act of ignore or attention diversion as his father, brother and sister-in-law walked in a procession in front of him.
"Harry had been chatting animatedly to Edoardo, jerking a thumb over his shoulder at one point, sharing a giggling laugh that seemed to involve his tongue placed between his teeth, and then doing a mutual, mirrored eye gaze with a matching lip clamp smile to Edo that seemed to signal mutual sympathy or empathy.
"Harry was looking up as Charles, William and Kate arrived to walk past but after looking at his father, Harry turned his head to speak to Eduardo again in a very odd way at a crucial point in the ceremony when all eyes and attention were on Charles and William's arrival."
The brothers looked worlds apart, with William taking centre stage as he planted a kiss on the monarch's cheek after he'd been crowned.
While Harry was left awkwardly smiling as he was forced to watch from his relegated seat.
King Charles
Obviously Charles was a bit busy and there was no time for father and son to have a chat.
But Harry was seen reacting as the crown was placed on his father's head at the historic Coronation.
The Duke of Sussex was seen watching intently as the archbishop raised St Edward's Crown above his father's head before crowning him.
When the congregation paid homage to the new monarch, Harry was seen, along with the other royals around him, speaking the words: "God save King Charles. Long live King Charles. May the King live forever."
However, some claimed that he stopped singing God Save the King as his father passed him during the procession.
One person tweeted: "Harry not singing National Anthem as King Processes Out."
Another added: "As the King left the cathedral I noticed that Harry was not singing to the National Anthem."
According to body language expert Darren Stanton, Harry experienced a "moment of sadness" as his father passed him during the coronation procession.
Mr Stanton noted that Harry appeared confident and elated throughout the ceremony, but displayed fleeting moments of sadness as his father passed him on his exit from the Abbey.
"Harry was confident and seemed genuinely quite elated throughout the ceremony," the expert told Betfair Bingo.
"He showed signs of pride towards his father, however, during the procession as King Charles passed Harry on his exit from the Abbey, Harry displayed fleeting moments of sadness within his facial expressions."
He added: "As he was on the outside looking on, it seemed Harry experienced feelings of nostalgia too. A noticeable moment was when Harry was seated in the Abbey, he was looking for a reassuring figure and appeared slightly out of sync compared to everyone else.
"We saw him adjusting his sleeves in a bid to reassure himself - a tell-tale pacifying gesture."
Princess Anne
A surprising person who did speak to Harry was Princess Anne - and they seemed to have a nice chat before the ceremony.
According to body language expert Judi James, the Duke of Sussex then started staring at Anne, who was sat in the row in front.
She explained: "His eye-gaze fixed on his aunt Anne who was chatting in the seats in front and then his head dropped down."
During the ceremony, viewers started to notice that Harry's face was being blocked by a giant read feather coming from Anne's hat.
Some audaciously suggested it may have been done on purpose - with people flocking to Twitter after noticing.
"Princess Anne's hat blocking views of Prince Harry during God Save The King… I AM SCREAMING," tweeted one person.
Another added: "Prince Harry is hidden behind the feather on Princess Anne's hat... last time it was a candle"
Princess Eugenie
One of the only family members who Harry has retained a strong relationship with is his cousin Eugenie.
Eugenie was the first and possible only royal visitor to see the Sussexes when they moved to California and Harry recalls attending a Halloween party with his cousin in his book Spare.
Prince Andrew's daughter also appeared in the couple's Netflix docuseries, cycling with Harry on the beach, and her son August is just four months older than Lili.
Harry arrived at Westminster Abbey with his cousin and her husband - and seemed to return to being a "joker".
Body language expert Judi James observed that Harry was seen mimicking his Eugenie's heavily pregnant state upon his arrival.
His action made Eugenie and husband Jack laugh - and showed a display of confidence around them from Harry.
Harry then used his body language to display a confident and upbeat approach as he made his way up the aisle.
Judi noted that Harry arrived with his cousins Beatrice and Eugenie, who have "remained friends despite the rifts in the royal family."
She told the Mirror: "Chatting first to Edo he then got the attention of Eugenie and Jack and we saw an incredible return of the joker prince as Harry grinned and used two hands cupped widely under his stomach to do what looked like a mime of Eugenie's heavily-pregnant state."
Jack Brooksbank
Harry spoke to Eugenie's husband more than anyone else at the Coronation.
Sat to the left of Jack, the pair were seen giggling as they shared a joke before the ceremony got started.
According to our lip reader, Harry joked about his quick visit to the UK and revealed what time he was going to be jetting back to the US.
With the Coronation falling on Archie's birthday, Harry decided to rush back to California to be with his son and the rest of his family.
According to a lip reader, Harry joked about his busy day and told Jack he would be leaving at "about quarter to four", to which Jack replied: "Oh really, when?"
Harry was also believed to have said "that's funny" to Brooksbank while smiling as they waited for Charles to arrive at Westminster Abbey.
