The Queen is to miss the ceremonial welcome during the Qatari state visit due to a lingering viral chest infection, according to Buckingham Palace.
It is understood the programme of the visit has been tweaked because Camilla, who contracted the infection after her long-haul trip to Australia and Samoa, has been left with significantly diminished reserves of energy.
Doctors have advised Camilla, 77, to take time to rest and recover fully.
The King and the Prince and Princess of Wales are set to welcome the Emir of Qatar and his wife to the UK on Tuesday during the traditional formal welcome outdoors on Horse Guards Parade.
Kate is taking part in her first state visit since her cancer diagnosis as part of her gradual return to public duties.
But the Queen will miss the outdoor event on Horse Guards Parade and she will not be present for the carriage ride back to Buckingham Palace.
Kate will meet Sheikh Tamim bin Hamad Al Thani and his wife, Sheikha Jawaher bint Hamad bin Suhaim Al Thani, with William in London, and accompany them to the parade ground to meet the waiting King and senior government figures.
Charles, Kate, William and their guests will afterwards take part in the carriage ride back to Buckingham Palace, attend a lunch and visit a Picture Gallery exhibition in the royal residence.
The Palace said Camilla’s programme had been changed, meaning she would miss both the ceremonial welcome and the carriage ride.
Camilla will be present at the lunch at the Palace on the royal party’s return and is hoping to view the exhibition in the Picture Gallery.
The Queen will join the King and their guests for photographs at the start of a glittering state banquet in the evening, and attend the event itself.
But she will take a short break before dinner while guests are being met in a receiving line.
Kate will not be attending the banquet, but William will be there.
