One of the biggest issues surrounding King Charles' Coronation is the incredibly awkward timing.
It is not yet known whether Prince Harry and Meghan Markle be part of the 2,000-strong congregation at Westminster Abbey, but they have received an official invitation.
Despite being the grandchildren of the new King, it is believed that Prince Archie and Princess Lilibet have not been invited, with sources citing that the children are "very young".
This will provide a major headache for Harry and Meghan as the date of the Coronation - May 6 - is also Archie's birthday.
There are reportedly fears that the Duke and Duchess of Sussex could 'upstage' Charles' Coronation if they try to go to heavy on Archie's birthday celebrations.
How the young prince's fourth birthday is celebrated appears to be a key issue for the Sussexes - but some royal fans have pointed out what Harry did when Archie turned three.
However, numerous people have pointed out that Harry was playing polo on his son's birthday last year.
Harry was riding horses with pal Nacho Figueras, the Argentinian actor who appeared in the Sussex's Netflix documentary and was also thanked in the acknowledgements in autobiography Spare.
Their team, 'Los Padres', won their match at the Santa Barbara polo club against rivals Mokarow farms.
"#PrinceHarry went to polo on #Archie's 3rd birthday…don't tell us you NOW want to celebrate it…on #KingCharlesCoronation," wrote on person.
Another added: "Considering last year Prince Harry, Archie's father, played polo on his birthday, I can't quite understand the upset."
"Given that Prince Harry played polo on Archie's birthday this year, I don't think they place too much importance on dedicating the whole day to celebrating their son's birthday," said a third.
Harry and Meghan allegedly have a number of varying demands which need to be fulfilled if they are to attend, including some recognition of their son's celebration.
"Archie's birthday falls on May 6th, coronation day and the Sussexes want the family to recognise that," a source told OK!.
"The Sussexes have asked for some kind of celebration or acknowledgement to be factored into the day's plans to ensure that his fourth birthday won’t get lost during the momentous day."
If they are to return in early May, insiders say they still intend to throw a party for their son - just like they would have done in California.
But they have been told they risk overshadowing Harry's father's big moment, Express.co.uk has reported, by doing things such as making a birthday announcement hours before the coronation.
The couple celebrated Lilibet Diana's birthday during the Queen's Platinum Jubilee last summer and went on to release a portrait of her.
Royal columnist Lee Cohen, who believes the weekend must only be about one thing, said: "It's terribly petty, but the Sussexes, who no longer have their royal platform, seem to relish any opportunity to attempt to upstage a royal occasion.
"It's not as if the Royal Family seek occasions to upstage the antics of the Sussexes, quite the opposite."
Archie and Lilibet may have new royal titles, but it doesn't look like they will be appearing at the Coronation along with their older cousins, Prince George, Princess Charlotte and possibly Prince Louis.
Charles' accession to the throne means the Sussex youngsters, who live in California with Harry and Meghan, have taken up their titles as Prince and Princess.
An insider told OK! that a major sticking point was how the Sussex children Archie, three, and one-year-old Lilibet were to be included on the day.
But the source explained that their inclusion in the ceremony has "never been a bone of contention" because small children don’t attend royal events of this scale "due to restlessness and tantrums".
Do you think Harry and Meghan are right to use Archie and Lilibet’s titles? Vote in our poll HERE to have your say.
According to royal historian and author Dr Tessa Dunlop, it would be "odd" if Archie has not been invited to the event.
She told True Royalty TV's The Royal Beat: ""If you look at the footage of the 1953 Coronation, who was very prominent, albeit briefly? Prince Charles. He was four.
"Archie on his fourth birthday is definitely not too young to attend the coronation. And if you want Meghan there, you need to invite her son."
