King Charles made a toast to Prince Archie after the Coronation and was gutted Prince Harry left straight away, according to an insider.
After the ceremony and the balcony appearance, the Royal Family gathered together for an intimate lunch away from the crowds.
Despite being invited to the luncheon, Harry decided to head back to California to be with wife Meghan Markle and his son, who was celebrating his fourth birthday.
Even though they are the grandchildren of the new King, it is believed that Archie and sister Princess Lilibet, one, were not invited, with sources citing that the children are "very young".
None of the royals released birthday messages, with Harry and Meghan also staying silent, but Charles did pay tribute to his grandson at the lunch.
An insider said that most members of the Royal Family 'breathed a sigh of relief' that Harry wasn't present, but Charles seemed 'genuinely quite disappointed that he didn't stay'.
The well-placed source said Prince William stood to congratulate his newly-crowned father before they began their meal.
After thanking everyone for their hard work, Charles reportedly raised a glass to his three grandchildren, Prince George, Princess Charlotte and Prince Louis.
But he wanted to remember 'those that weren't there' and wished Archie a very happy birthday 'wherever he was'.
"It was apparently a very sweet moment," the source told Daily Mail.
As well as the new King and Queen, there were other members of the Royal Family present at the lunch.
Camilla's close relatives also attended, including her children, Tom Parker Bowles and Laura Lopes, and grandchildren, Lola, Freddy, Eliza, Louis and Gus.
The Queen's sister Annabel and best friend Lady Landsdowne, who both served as her attendants at the Coronation, were also seated at the table.
Apparently, the family enjoyed canapes including mini broad bean and tarragon Coronation quiches, which was the official dish of the Coronation weekend.
But there was a more 'modern take' Coronation chicken canapes as the King and Queen are not fans of the famous dish.
The adults were also offered glasses of fizz, but not much alcohol was served as everyone needed to 'keep a clear head'.
No one stayed at the palace for too long as it is still undergoing extensive renovations, so most of the royals headed over to Windsor Castle for a private drinks party.
Princess Kate's family also got invited - with parents Michael and Carole Middleton and siblings Pippa and James turning up.
Staff put on a 'running buffet' at Buckingham Palace while the official Coronation pictures were being taken by society photographer Hugo Burnand.
Instead of being forced to sit inside Westminster Abbey for the ceremony, the Sussex kids probably had a much better time enjoying a fun-filled "intimate" birthday party for Archie.
The Royal Family usually post a birthday message to Archie on their social media channels, but they are yet to provide one this year.
The young prince hasn't always had the best of birthdays, with the Royal Family awkwardly forced to re-use old photos of Harry and Meghan's son last year.
According to the Mail, officials at the palace were left feeling uncomfortable because they didn't have an up-to-date picture of Archie to accompany his birthday messages on social media.
Instead they were forced to use photos from just after he was born or from his official christening.
A source said: "The truth is the Prince of Wales has barely seen his grandson twice since he was born. In fact every member of Harry’s family can easily count on one hand the number of times they saw Archie after he was born and before the family left the UK. It’s a very sad situation."
