The Duke and Duchess of Sussex have been invited to appear on the Buckingham Palace balcony during the Platinum Jubilee celebrations but can have "no formal role", it is understood.
If the couple opt to travel to London to join their family in celebrating the Queen's 70 years on the throne, they will appear at family events, which include the traditional balcony appearance as well as a service of thanksgiving at St Paul's Cathedral.
However, as non-working members of "the firm", they cannot take part in Trooping the Colour or play any central role at the various events throughout the four-day Bank Holiday weekend.
While the Queen's increasing frailty means she is unlikely to make many public appearances, it is hoped that at the very least she will take part in the Trooping procession, either in a carriage or watching from a dais, and then appear on the palace balcony alongside her wider family for the traditional fly-past on June 2. The moment will be particularly poignant as it will likely mark the last big family balcony appearance of her reign.
Aides concede that while the Sussexes' presence would mean a lot to Her Majesty, it would take a leap of faith from all sides after the damaging allegations the couple have made in a string of television interviews since moving abroad.
Prince Harry would also have to swallow his pride over the ongoing legal wrangle concerning his security after saying his family would not be safe visiting the UK following the Government's decision not to provide them with police protection.
A spokesman for the Sussexes said yesterday that they were not in a position to discuss travel plans.
Meanwhile, Buckingham Palace is making contingency plans for Jubilee events to take place in the absence of the Queen, with younger members of the royal family taking her place.
A series of meetings has taken place this month as palace aides seek to allocate specific roles to members of the family.
The Queen, who turns 96 on Thursday, is determined to take part in the four-day celebration and plans to attend as many events as possible.
However, her struggles with mobility issues mean that in reality, her participation is likely to be minimal.
One of the most important events for the Queen will be the service of thanksgiving at St Paul's Cathedral on June 3.
Palace aides are working on plans to ensure that she can attend with dignity, as she will be unable to walk up the many steps at the main entrance.
Staff are considering how she can best travel to the service in comfort and make her way into a side entrance of the Cathedral without being photographed having difficulty walking.
For Her Majesty, a horse racing fanatic, the Epsom Derby on June 4 will also be a highlight of the festivities, although the logistics could prove challenging.
She would usually be driven down the home straight before taking a short walk to the stands for a receiving line, but plans are being put in place for her to be dropped off as close to the grandstand as possible, where she can then take a lift to her box.
Despite earlier reports that the Duke of York could accompany her, it is understood the Duchess of Cornwall, who is also "absolutely besotted" by racing, has been earmarked to attend alongside her.
The Prince of Wales is expected to give a speech at the Platinum Party at the Palace, when he will thank his mother for her service over the past seven decades.
Prince Charles will attend almost all of the Jubilee events, representing the Queen where appropriate if she is unable to attend.
However, aides are keen to point out that even in the Queen's absence, "it is her party" and that everything will very much take place in her honour.