Queen Camilla has revealed she suffered from pneumonia following a recent overseas trip and is now experiencing post-viral fatigue.
The Queen is missing outdoor elements of the Qatari state visit as doctors have urged her to take more time to recover.
The 77-year-old was notably absent from Tuesday's outdoor ceremonial welcome at Horse Guards Parade.
She instead arrived at Buckingham Palace's Grand Entrance shortly before the ceremony, offering a smile as she stepped from her car.
Queen Camilla has revealed she suffered from pneumonia following a recent overseas trip and is now experiencing post-viral fatigue.
PA
Inside the Palace's Grand Hall, she waited to greet the Emir of Qatar and his wife.
The Queen contracted her chest infection following a long-haul trip to Australia and Samoa.
She has since been forced to cancel several engagements, including the Royal Variety Performance, the Gladiator II premiere and the Remembrance Day service at the Cenotaph.
Inside the Palace's Grand Hall, she waited to greet the Emir of Qatar and his wife.
PA
King Charles attended both the Royal Variety Performance and the Gladiator II premiere on his own as solo engagements.
It is understood the Queen's condition was viral rather than bacterial pneumonia, and she did not require hospitalisation.
While she no longer has pneumonia, palace sources indicate she is experiencing bouts of extreme tiredness during her recovery.
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While she no longer has pneumonia, palace sources indicate she is experiencing bouts of extreme tiredness during her recovery.
PA
After Camilla withdrew from the Royal Variety Performance, a Palace spokesman said: "Following a recent chest infection, The Queen continues to experience some lingering post-viral symptoms, as a result of which doctors have advised that, after a busy week of engagements, Her Majesty should prioritise sufficient rest.
"With great regret, she has therefore withdrawn from attendance at tonight’s Royal Variety Performance."
Camilla also pulled out of the Remembrance Sunday Weekend events as a result of the "lingering" symptoms.
